Negative electrode for lithium metal battery and lithium metal battery comprising the same

ABSTRACT

A negative electrode for a lithium metal battery including: a lithium metal electrode including a lithium metal or a lithium metal alloy; and a protective layer on at least portion of the lithium metal electrode, wherein the protective layer has a Young&#39;s modulus of about 106 pascals or greater and includes at least one particle having a particle size of greater than 1 micrometer to about 100 micrometers, and wherein the at least one particle include an organic particle, an inorganic particle, an organic-inorganic particle, or a combination thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of U.S. patent application Ser. No.15/581,072, filed on Apr. 28, 2017, which claims priority to and thebenefit of Korean Patent Application No. 10-2016-0053531, filed on Apr.29, 2016, and Korean Patent Application No. 10-2017-0049894, filed onApr. 18, 2017, in the Korean Intellectual Property Office, and all thebenefits accruing therefrom under 35 U.S.C. § 119, the contents of whichin their entirety are incorporated herein by reference.

BACKGROUND 1. Field

The present disclosure relates to a negative electrode for a lithiummetal battery and a lithium metal battery including the negativeelectrode.

2. Description of the Related Art

Lithium secondary batteries are high-performance batteries having arelatively high energy density as compared to other types of secondarybatteries, and are applicable to various fields including, for example,electric vehicles.

A lithium secondary battery may use a lithium metal thin film as anegative electrode. When a lithium metal thin film is used as thenegative electrode, the negative electrode may react with the liquidelectrolyte during charging or discharging of the battery due to thehigh reactivity between the lithium metal and the electrolyte, anddendritic growth may occur on the lithium metal thin film negativeelectrode. Accordingly, a lithium secondary battery including a lithiummetal thin film may have reduced lifetime and stability. Therefore,there is a need for a lithium secondary battery having improvedproperties.

SUMMARY

Provided is a negative electrode for a lithium metal battery, thenegative electrodes including a protective layer with desirablemechanical properties.

Provided is a lithium metal battery with improved cell performance andincluding the of the negative electrodes.

According to an aspect of an embodiment, a negative electrode for alithium metal battery includes: a lithium metal electrode includinglithium metal or a lithium metal alloy; and a protective layer on atleast a portion of the lithium metal electrode, wherein the protectivelayer has a Young's modulus of about 106 pascals (Pa) or greater andincludes at least one particle having a particle size of greater than 1micrometer to about 100 micrometers, and wherein the at least oneparticle includes an organic particle, an inorganic particle, anorganic-inorganic particle, or a combination thereof.

According to an aspect of another embodiment, a lithium metal batteryincludes a positive electrode, a negative electrode, and an electrolytebetween the positive electrode and the negative electrode, wherein thenegative electrode includes: a lithium metal electrode comprisinglithium metal or a lithium metal alloy; and a protective layer on atleast a portion of the lithium metal electrode, wherein the protectivelayer has a Young's modulus of about 10⁶ Pascals or greater andcomprises at least one particle having a particle size of greater than 1micrometer to about 100 micrometers or less, and wherein the at leastone particle comprises an organic particle, an inorganic particle, anorganic-inorganic particle, or a combination thereof.

Also disclosed is method of manufacturing a negative electrode for alithium metal battery, the method including: providing a lithium metalelectrode including lithium metal or a lithium metal alloy; anddisposing a protective layer on at least a portion of the lithium metalelectrode to manufacture the negative electrode, wherein the protectivelayer has a Young's modulus of about 106 pascals or greater andcomprises at least one particle having a particle size of greater than 1micrometer to about 100 micrometers, and wherein the at least oneparticle comprises an organic particle, an inorganic particle, anorganic-inorganic particle, or a combination thereof.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIGS. 1A to 1D are schematic views illustrating various structures of anembodiment of a negative electrode for a lithium metal battery;

FIGS. 1E and 1F are schematic views explaining the theoretical principlebehind using a protective layer on a negative electrode for suppressingand guiding dendritic growth in a lithium metal battery, according to anembodiment;

FIGS. 1G to 1K are schematic views illustrating structures of anembodiment of a lithium metal battery;

FIG. 1L is a schematic view illustrating an embodiment of a protectivefunction of a protective layer for a lithium metal electrode in anegative electrode for a lithium metal battery according to anembodiment, when microspheres in the protective layer have an averageparticle diameter of greater than about 1 μm to about 100 μm or less;

FIG. 1M is a schematic view illustrating an embodiment of a protectivefunction of a protective layer for a lithium metal electrode in anegative electrode for a lithium metal battery, when microspheres in theprotective layer have an average particle diameter of about 1 μm orless;

FIGS. 2A to 2D are scanning electron microscopic (SEM) images of thenegative electrode of Example 1;

FIGS. 3A to 3C are SEM images of the negative electrode of Example 4;

FIG. 3D is an SEM image of the negative electrode of Example 22;

FIG. 4A is a schematic view illustrating the structure of a lithiummetal battery of Example 9, in which the negative electrode of thelithium metal battery was formed on a copper thin film used as anegative electrode current collector;

FIGS. 4B and 4C are SEM images of the surface of the negative electrodein the lithium metal battery of Example 9;

FIG. 4D is an SEM image of a cross-section of the lithium metal batteryof Example 9, which shows a lithium deposition layer formed on thenegative electrode of the lithium metal battery;

FIG. 5A is a schematic view illustrating the structure of the lithiummetal battery of Comparative Example 1, in which a negative electrode ofthe lithium metal battery was formed on a copper thin film used as anegative electrode current collector;

FIGS. 5B and 5C are is SEM images of a surface of the negative electrodein the lithium metal battery of Comparative Example 1;

FIG. 5D are a SEM image of a cross-section of the lithium metal batteryof Comparative Example 1, illustrating a lithium deposition layer formedon the lithium metal electrode of the lithium metal battery;

FIG. 6 is a Nyquist graph of real impedance (Z″, ohm) versus imaginaryimpedance (Z′, ohm), illustrating the results of an impedancemeasurement on the lithium metal batteries of Example 17 and ComparativeExample 1;

FIG. 7 is a graph of discharge capacity (milliampere hours, mAh) versuscycle number, illustrating the change in capacity retention rate in thelithium metal batteries of Example 9 and Comparative Example 1;

FIGS. 8A and 8B are graphs of discharge capacity (mAh) versus cyclenumber, showing the change in discharge capacity in the lithium metalbatteries of Example 17 and Comparative Example 1;

FIG. 8C is a graph of cycle efficiency (%) versus cycle number, showingthe change in coulombic efficiency in the lithium metal batteries ofExample 17 and Comparative Example 1; and

FIGS. 9A to 9C are schematic views of negative electrodes illustratingthe arrangement of microsphere particles as a protective layer on asurface of a lithium metal electrode, according to various embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of anegative electrode for a lithium metal battery and a lithium metalbattery including a negative electrode according to any of theembodiments, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout. In this regard, the present embodiments may have differentforms and should not be construed as being limited to the descriptionset forth herein. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the invention to those skilled in the art. Accordingly, theembodiments are described below, by referring to the figures, to explainvarious aspects.

When an element or layer is referred to as being “on” or “above” anotherelement or layer, it includes the element or layer that is directly orindirectly in contact with the another element or layer. Thus it will beunderstood that when an element is referred to as being “on” anotherelement, it can be directly on the other element or intervening elementsmay be present therebetween. In contrast, when an element is referred toas being “directly on” another element, there are no interveningelements present.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, “a first element,” “component,” “region,” “layer” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “At least one” is not to be construed as limiting “a” or“an.” “Or” means “and/or.” As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.Expressions such as “at least one of,” when preceding a list ofelements, modify the entire list of elements and do not modify theindividual elements of the list. It will be further understood that theterms “comprises” and/or “comprising,” or “includes” and/or “including”when used in this specification, specify the presence of statedfeatures, regions, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, regions, integers, steps, operations, elements,components, and/or groups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±10% or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

As used herein, “average particle size” or “average particle diameter”or “D50 particle size” refers to a particle diameter corresponding to50% of the particles in a distribution curve in which particles areaccumulated in the order of particle diameter from the smallest particleto the largest particle and a total number of accumulated particles is100%. The average particle size may be measured by methods known tothose of skill in the art. For example, the average particle size may bemeasured with a particle size analyzer or may be measured by using atransmission electron microscope (TEM) or a scanning electron microscope(SEM) image. As an example of other measuring methods, average particlesize may be measured with a measurement device using dynamic lightscattering, the number of particles within predetermined size ranges maybe counted, and an average particle diameter may be calculatedtherefrom.

As used herein the term “porosity” is used to refer to a measure of theempty space (i.e., voids or pores) in a material and is determined as apercentage of the volume of voids in a material based on the totalvolume of the material.

According to an embodiment of the present disclosure, there is provideda negative electrode for a lithium metal battery, the negative electrodeincluding: a lithium metal electrode including lithium metal or alithium metal alloy; and a protective layer disposed on at least aportion of the lithium metal electrode, wherein the protective layer hasa Young's modulus of about 10⁶ Pa or greater and includes at least oneparticle having a particle size of greater than about 1 micrometer (μm)to about 100 μm.

The lithium metal or a lithium metal alloy has a relatively highelectric capacity per unit weight, and thus may be used to implement ahigh-capacity battery. However, using such a lithium metal or lithiummetal alloy may cause dendritic growth during the deposition/dissolutionof lithium ions during charging and discharging of the battery andconsequently results in a short circuit between the positive andnegative electrodes. An electrode including a lithium metal or lithiummetal alloy may be highly reactive with the electrolyte, and thus mayresult in a side reaction between lithium metal or lithium metal alloyand the electrolyte. Due to these side reactions, the cycle lifetime ofa battery is reduced. To address this problem, a protective layer whichprotects the surface of the electrode including the lithium metal orlithium metal alloy has been developed.

Accordingly, the present inventors have advantageously developed aprotective layer, which includes a lithium salt or a liquid electrolyte.When the protective layer includes a liquid electrolyte, the liquidelectrolyte may form ion conducting paths so that the negative electrodemay have improved conductivity. Thus, a lithium metal battery withstable cycle characteristics may be manufactured using a negativeelectrode including the protective layer.

The liquid electrolyte may include an organic solvent, an ionic liquid,and a lithium salt. The liquid electrolyte may occupy about 30 volumepercent (%) to about 60 volume % of the total volume of the protectivelayer. For example, the liquid electrolyte may occupy about 35 volume %to about 55 volume %, or about 40 volume % to about 50 volume % of thetotal volume of the protective layer.

In case the finally obtained protective layer includes a liquidelectrolyte, the liquid electrolyte may be added to the preparation ofthe protective layer. Otherwise, the protective layer does not includethe liquid electrolyte during the preparation of the protective layer.However, after the lithium metal battery using the proactive layerwithout the liquid electrolyte is operated, the finally obtainedprotective layer may be contain in which the liquid electrolytecontained in the lithium metal battery is transferred.

In some embodiments, the at least one particle in the protective layermay have a particle size of 1.1 μm to about 75 μm, for example, about1.3 μm to about 50 μm, or about 1.3 μm to about 25 μm, or about 1.5 μmto about 20 μm, or about 1.5 μm to about 10 μm.

In some embodiments, the at least one particle includespoly(styrene-divinylbenzene) copolymer microspheres having an averageparticle diameter of about 3 μm and poly(styrene-divinylbenzene)copolymer microspheres having an average particle diameter of about 8 μmin a weight ratio of 1:1. Alternatively, the at least one particleincludes poly(styrene-divinylbenzene) copolymer microspheres having anaverage particle diameter of about 3 μm and poly(styrene-divinylbenzene)copolymer microspheres having an average particle diameter of about 1.3μm in a weight ratio of 1:1. The particle includespoly(styrene-co-divinylbenzene) copolymer microspheres having an averageparticle diameter of about 3 μm and poly(styrene-co-divinylbenzene)copolymer microspheres having an average particle diameter of about 1.1μm at a weight ratio of 1:1.

According to an embodiment, the particle is a microsphere having amono-modal particle diameter distribution. The mono-modal particlediameter distribution may be defined by a standard deviation of lessthan 40%, for example, 20% or less, or 10% or less, and having a rangeof about 1% or greater to less than about 40%, or in a range of about 2%to about 25%, or in a range of about 3% to about 10%, when analyzed by aparticle diameter analyzer (Dynamic Light Scattering: DLS, Nicomp 380).

The protective layer may have a Young's modulus of about 106 Pa orgreater, for example, about 107 Pa or greater, or about 10⁸ Pa orgreater. The Young's modulus may be from about 10⁶ Pa to about 10¹¹ Pa,or from about 107 Pa to about 10¹⁰ Pa, or from about 107 Pa to about 109Pa. When the protective layer has a Young's modulus within these ranges,the protective layer may have good tensile strength and good mechanicalproperties.

The Young's modulus is used as a measure of the stiffness of theprotective layer and has the same meaning as a “tensile modulus.” Thetensile modulus of the protective layer may be measured according toASTM D412 using dynamic mechanical analysis system (DMA800; availablefrom TA Instruments) as follows. Protective layer samples are preparedaccording to the ASTM standard D412 (Type V specimens), and variationsin strain with respect to stress in a protective layer sample aremeasured at a temperature of about 25° C., a relative humidity of about30%, and a rate of 5 millimeters (mm) per minute, thereby to obtain astress-strain curve. The tensile modulus of the protective layer iscalculated from the slope of the stress-strain curve.

The at least one particle in the protective layer may have across-linked structure. The at least one particle in the protectivelayer may have a chemically cross-linked structure or a physicallycross-linked structure.

The protective layer may include the at least one particle having achemically or physically cross-linked structure. The at least oneparticle may include, for example, an organic particle of a cross-linkedpolymer obtained from a polymer having a cross-linkable functionalgroup, an inorganic particle having a cross-linked structure due to across-linkable functional group on a surface thereof, or the like. Thecross-linkable functional group, which is involved in a cross-linkingreaction, may be, for example, an acryl group, a methacryl group, avinyl group, or the like.

Cross-linking may be induced by heating or by irradiation withultraviolet (UV) light. The heating or UV light irradiation may beperformed so as not to adversely affect the lithium metal electrode.

A particle having a chemically cross-linked structure refers to aparticle in which cross-linking has occurred using chemical methods(e.g., chemical agents) to facilitate bonding of cross-linkablefunctional groups present in a material for forming the particle. Aparticle having a physically cross-linked structure refers to a particlein which cross-linking has occurred using physical methods, for example,heating a polymer forming the particle until it reaches its glasstransition (Tg) temperature, in order to facilitate bonding ofcrosslinkable functional groups, i.e., cross-links which are not formedusing chemical agents. The cross-linking may occur within the particleitself and may also occur between adjacent particles in the protectivelayer.

The lithium metal or lithium metal alloy in the lithium metal electrodemay have a thickness of about 100 μm or less, and in some embodiments,about 80 μm or less, or about 50 μm or less, or about 30 μm or less, orabout 20 μm or less, and in some other embodiments, about 0.1 μm toabout 60 μm. For example, the lithium metal or lithium metal alloy mayhave a thickness of about 1 μm to about 25 μm, and in some embodiments,about 5 μm to about 20 μm, and in some other embodiments, about 10 μm toabout 20 μm.

The shape of the at least one particle in the protective layer mayinclude a spherical shape, a rod shape, an ellipsoidal shape, a radialshape, or the like. A combination comprising at least one of theforegoing may also be used.

When the at least one particle in the protective layer has a sphericalshape, the at least one particle in the protective layer may be amicrosphere having an average particle diameter of greater than 1 μm toabout 100 μm. The microspheres may have an average particle diameter of1.1 μm to about 75 μm, for example, about 1.3 μm to about 50 μm, orabout 1.3 μm to about 25 μm, or about 1.5 μm to about 20 μm, or about1.5 μm to about 10 μm.

If the at least one particle in the protective layer has a particle sizegreater than about 100 μm, the protective layer and a lithium metalbattery including the protective layer may both become too thick, andthus, the lithium metal battery may have lower energy densitycharacteristics. Furthermore, if the protective layer is too thick, theprotective layer may also have an increased porosity, and as a resultthe liquid electrolyte may be more likely to contact the lithium metalelectrode.

If the at least one particle in the protective layer has a particle sizeof about 1 μm or less, a lithium metal battery including the protectivelayer with such small particles may have poor lithium deposition densitycharacteristics as compared to a lithium metal battery with a protectivelayer including at least one particle having a particle size greaterthan about 1 μm and about 100 μm or less.

As used herein, the term “size” or “particle size” may refer to anaverage particle diameter when the particle has a spherical shape, andrefers to the length of a major axis when the particle has a rod shapeor an elliptical shape.

FIG. 1L is a schematic view of a negative electrode for a lithium metalbattery according to an embodiment, illustrating a protective functionof a protective layer for a lithium metal electrode in the negativeelectrode, when microspheres in the protective layer have a particlediameter greater than about 1 μm and about 100 μm or less. FIG. 1M is aschematic view of a negative electrode for a lithium metal battery,illustrating a protective function of a protective layer for a lithiummetal electrode in a negative electrode for a lithium metal battery whenmicrospheres in the protective layer have an average particle diameterof about 1 μm or less.

Referring to FIG. 1L, a protective layer 12 including microspheres 13 amay be stacked on a lithium metal electrode 11. A surface coatingfraction of the microspheres 13 a in the protective layer 12 of thelithium metal electrode 11 and the gap between the microspheres 13 a arefactors which directly impact the protective function of the protectivelayer 12 of the lithium metal electrode 11. The surface coating fractionrefers to the portion of the surface of the lithium metal electrodewhich includes the protective layer relative to a total surface area ofthe lithium metal electrode. The surface coating fraction may be about80%, or about 85%, or about 90%, or about 95%, or about 100% of thetotal surface area of the lithium metal electrode.

The lithium metal electrode 11 may be, for example, a lithium metal. Asshown in FIG. 1L, the lithium metal electrode 11 may be thin enough tohave soft characteristics. The lithium metal electrode 11 may have athickness of, for example, about 5 μm to about 50 μm, or about 10 toabout 30 μm, or about 15 μm to about 25 μm. The lithium metal electrode11 may have a surface step difference of about ±1 μm. To protect thelithium metal electrode 11 having such a surface step difference, it maybe effective to use the microspheres 13 a having an average particlediameter greater than 1 μm to about 100 μm in the protective layer 12.

Meanwhile, as illustrated in FIG. 1M, when the protective layer 12 onthe lithium metal electrode 11 includes microspheres having an averageparticle diameter of about 1 μm or less, for example, about 5 nanometers(nm) to about 300 nm, the aggregation and surface coating fraction ofthe microspheres may be poor, so that the protective layer 12 may havean increased porosity, and liquid electrolyte may be more likely tocontact the lithium metal.

The particle size may mean an average particle diameter when the atleast one particle in the protective layer 12 is of a spherical shape,or a length of the major axis when the at least one particle in theprotective layer 12 is of a rod shape. For example, when the at leastone particle in the protective layer 12 has a rod shape, a minor tomajor axis ratio of the particle may be, for example, about 1:1 to about1:30, or about 1:2 to about 1:25, or about 1:5 to about 1:20.

The at least one particle in the protective layer 12 may include anypolymer that may be suitable to form protective layers.

In some embodiments, the at least one particle in the protective layer12 may include a polymer having low wettability against a liquidelectrolyte.

The at least one particle in the protective layer 12 may include apolymer including a polystyrene homopolymer, a copolymer including astyrene repeating unit, a copolymer including a repeating unit having across-linkable functional group, a cross-linked polymer, or acombination thereof. For example, the at least one particle in theprotective layer 12 may be a polymer, e.g., a homopolymer or acopolymer, including a styrene repeating unit. When the at least oneparticle in the protective layer is a polymer including a styrenerepeating unit, which has hydrophobicity and essentially no wettabilityto the electrolyte, and the polymer does not adversely affect thelithium metal electrode, then the reactivity of the lithium metalelectrode with the electrolyte may be suppressed.

The at least one particle may include a polymer including polystyrene, apoly(styrene-divinylbenzene) copolymer, a poly(methylmethacrylate-divinylbenzene) copolymer, a poly(ethylmethacrylate-divinylbenzene) copolymer, a poly(pentylmethacrylate-divinylbenzene) copolymer, a poly(butylmethacrylate-divinylbenzene) copolymer, a poly(propylmethacrylate-divinylbenzene) copolymer, apoly(styrene-ethylene-butylene-styrene) copolymer, a poly(styrene-methylmethacrylate) copolymer, a poly(styrene-acrylonitrile) copolymer, apoly(styrene-vinylpyridine) copolymer, apoly(acrylonitrile-butadiene-styrene) copolymer, apoly(acrylonitrile-ethylene-propylene-styrene) copolymer, a poly(methylmethacrylate-acrylonitrile-butadiene-styrene) copolymer, a poly((C₁-C₉alkyl) methacrylate-butadiene-styrene) copolymer, a poly(styrene-(C₁-C₉alkyl) acrylate) copolymer, and a poly(acrylonitrile-styrene-(C₁-C₉alkyl) acrylate) copolymer, or a combination thereof. The polymer mayinclude a cross-linked polymer. The cross-linked polymer refers to, forexample, a poly(styrene-divinylbenzene) copolymer, a poly(methylmethacrylate-divinylbenzene), a cross-linked product of apoly(styrene-divinylbenzene) copolymer, a cross-linked product of apoly(methyl methacrylate-divinylbenzene), or a combination thereof. Acombination comprising at least one of the foregoing may also be used.In a copolymer including a styrene repeating unit, the amount of thestyrene repeating unit may be from about 65 to 99 parts by weight, andin some embodiments, about 80 to 99 parts by weight, and in someembodiments, about 90 to 99 parts by weight, and in some otherembodiments, about 96 to 99 parts by weight, based on 100 parts byweight of the copolymer.

In a copolymer including a divinylbenzene as a repeating unit, theamount of divinylbenzene may be from about 1 to 35 parts by weight, andin some embodiments, about 1 to 20 parts by weight, and in someembodiments, about 1 to 10 parts by weight, and in some otherembodiments, about 1 to 4 parts by weight, and in some otherembodiments, about 3 to 7 parts by weight, and in still otherembodiments, about 5 parts by weight, based on 100 parts by weight ofthe copolymer.

In each of the above-listed copolymers of poly(methylmethacrylate-divinylbenzene) copolymer, poly(ethylmethacrylate-divinylbenzene) copolymer, poly(pentylmethacrylate-divinylbenzene) copolymer, poly(butylmethacrylate-divinylbenzene) copolymer, and poly(propylmethacrylate-divinylbenzene) copolymer, the amount of the methylmethacrylate, ethyl methacrylate, pentyl methacrylate, butylmethacrylate, or propyl methacrylate repeating unit may be from about 65to 99 parts by weight, and in some embodiments, about 80 to 99 parts byweight, and in some embodiments, about 90 to 99 parts by weight, and insome other embodiments, about 96 to 99 parts by weight, based on 100parts by weight of the copolymer.

In each of the above-listed poly(styrene-ethylene-butylene-styrene)copolymer, poly(styrene-methyl methacrylate) copolymer,poly(styrene-acrylonitrile) copolymer, poly(styrene-vinylpyridine)copolymer, poly(acrylonitrile-butadiene-styrene) copolymer,poly(acrylonitrile-ethylene-propylene-styrene) copolymer, poly(methylmethacrylate-acrylonitrile-butadiene-styrene) copolymer, poly((C₁-C₉alkyl) methacrylate-butadiene-styrene) copolymer, poly(styrene-(C₁-C₉alkyl) acrylate) copolymer, and poly(acrylonitrile-styrene-(C₁-C₉ alkyl)acrylate) copolymer, the amount of the styrene repeating unit may befrom about 65 to 99 parts by weight, and in some embodiments, about 80to 99 parts by weight, and in some embodiments, about 90 to 99 parts byweight, and in some other embodiments, about 96 to 99 parts by weight,based on 100 parts by weight of the copolymer. When the above-listedcopolymers are a ternary or quaternary copolymer, the non-styrenerepeating units may be combined in any of a variety of ratios to make upthe balance of the copolymer based upon the amount of the styrenerepeating units. The above-listed polystyrene copolymers may include ablock copolymer, a random copolymer, an alternating copolymer, a graftcopolymer, and the like. A combination comprising at least one of theforegoing polystyrene copolymers may also be used. These copolymers mayhave a weight average molecular weight of about 10,000 Daltons to about50,000 Daltons.

The weight average molecular weight may be measured by methods known tothose of skill in the art. For example, the weight average molecularweight is measured by Gel permeation chromatography (GPC).

In the block copolymer, a block including a first repeating unit mayhave a weight average molecular weight of about 10,000 Daltons orgreater, and in some embodiments, about 10,000 to 510,000 Daltons, insome other embodiments, about 15,000 to about 400,000 Daltons, and insome embodiments about 20,000 to about 200,000 Daltons. The amount ofthe block including the first repeating unit may be about 20 to 50 partsby weight, or for example, about 20 to about 40 parts by weight, or forexample, about 22 to 30 parts by weight, based on 100 parts by weight ofthe block copolymer. When using such a polymer block, the protectivelayer may have good mechanical properties, for example, improvedstrength.

In the block copolymer, a block including a second repeating unit mayhave a weight average molecular weight of about 10,000 Daltons orgreater, and in some embodiments, about 10,000 to 510,000 Daltons, andin some other embodiments, about 15,000 to 400,000 Daltons. Theprotective layer may have improved ductility, elasticity, and strengthcharacteristics. When using a block having a weight average molecularweight within these ranges, the protective layer may have improvedductility, elasticity, and strength characteristics.

The block copolymer may include a diblock copolymer (A-B), a triblockcopolymer (A-B-A′ or B-A-B′), or a combination thereof.

The at least one particle in the protective layer may include apolyvinyl pyridine, polyvinyl cyclohexane, polyglycidyl acrylate,poly(2,6-dimethyl-1,4-phenylene oxide), polyolefin, poly(tert-butylvinyl ether), polycyclohexyl vinyl ether, polyvinyl fluoride,poly(styrene-maleic anhydride) copolymer, polyglycidyl methacrylate,polyacrylonitrile, a polymeric ionic liquid or a combination thereof.

The at least one particle in the protective layer may include apoly(styrene-divinylbenzene) copolymer, a poly(methylmethacrylate-divinylbenzene) copolymer, a poly(ethylmethacrylate-divinylbenzene) copolymer, a poly(pentylmethacrylate-divinylbenzene) copolymer, a poly(butylmethacrylate-divinylbenzene) copolymer, a poly(propylmethacrylate-divinylbenzene) copolymer, a poly(methylacrylate-divinylbenzene) copolymer, a poly(ethylacrylate-divinylbenzene) copolymer, a poly(pentylacrylate-divinylbenzene) copolymer, poly(butyl acrylate-divinylbenzene)copolymer, a poly(propyl acrylate-divinylbenzene) copolymer, apoly(pentyl acrylate-divinylbenzene) copolymer, apoly(acrylonitrile-butadiene-styrene) copolymer, or a combinationthereof. A combination comprising at least one of the foregoing may alsobe used.

When the at least one particle in the protective layer includes across-linked polymer as described above, individual particles may beconnected to each other due to cross-linking between the particles, andas a result, the protective layer may have improved mechanical strength.The protective layer may have a degree of cross-linking of about 10 to30%, for example, about 12 to 28%, for example about 15% to about 25%.

Structures of negative electrodes for lithium metal batteries, accordingto exemplary embodiments, will be described with reference to FIGS. 1Ato 1D. In FIGS. 1A to 1D, as a non-limiting example, a particle 13 in aprotective layer 12 may have a microspheric shape.

Referring to FIG. 1A, a negative electrode according to an embodimentmay include a lithium metal electrode 11 on a current collector 10,wherein the lithium metal electrode 11 may include lithium metal or alithium metal alloy. The protective layer 12 may be on the lithium metalelectrode 11. The protective layer 12 may include particles 13 that havegaps (i.e., space) between the particles 13, and ions may be transportedthrough the gaps. Thus, using the protective layer 12, the negativeelectrode may have improved ion conductivity. Furthermore, the gaps, forexample, pores structures between the particles 13, may provide a spacefor lithium dendritic growth and act as a guide for growth of lithiumdendrites.

The lithium metal alloy may include a lithium metal and ametal/metalloid alloyable with lithium metal or an oxide of themetal/metalloid. Examples of the metal/metalloid alloyable with lithiummetal or an oxide of thereof include Si, Sn, Al, Ge, Pb, Bi, Sb, a Si—Yalloy (wherein Y is an alkaline metal, an alkaline earth metal, a Group13 to 16 element, a transition metal, a rare earth element, or acombination thereof, except for Si), a Sn—Y alloy (wherein Y is analkaline metal, an alkaline earth metal, a Group 13 to 16 element, atransition metal, a rare earth element, or a combination thereof, exceptfor Sn), MnOx (wherein 0<x≤2), or a combination thereof.

Y may include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba),radium (Ra), scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr),hafnium (Hf), rutherfordium (Rf), vanadium (V), niobium (Nb), tantalum(Ta), dubnium (Db), chromium (Cr), molybdenum (Mo), tungsten (W),seaborgium (Sg), technetium (Tc), rhenium (Re), bohrium (Bh), iron (Fe),lead (Pb), ruthenium (Ru), osmium (Os), hassium (Hs), rhodium (Rh),iridium (Ir), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag),gold (Au), zinc (Zn), cadmium (Cd), boron (B), aluminum (Al), gallium(Ga), tin (Sn), indium (In), thallium (Tl), germanium (Ge), phosphorus(P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur (S), selenium(Se), tellurium (Te), polonium (Po), or a combination thereof. Forexample, the oxide of a metal/metalloid alloyable with lithium metal maybe a lithium titanium oxide, a vanadium oxide, a lithium vanadium oxide,Sn₂, SiOx (wherein 0<x<2), or the like. A combination comprising atleast one of the foregoing may also be used.

Referring to FIG. 1B, the particles 13 may be surrounded by an ionconductive polymer 14. Although not illustrated, a liquid electrolytemay be present in the gaps between the particles 13.

The ion conductive polymer 14, which may be in the protective layer 12,may improve the intensity of the protective layer 12, and serve as abinder. The amount of the ion conductive polymer 14 may be about 10parts by weight or less, and in some embodiments, about 5 parts byweight or less, or about 2 parts by weight or less, and in some otherembodiments, may be about 1 to about 10 parts by weight, or about 1 toabout 5 parts by weight, or about 1 to about 2 parts by weight, based on100 parts by weight of the particles 13. When the amount of the ionconductive polymer 14 is within these ranges, the protective layer 12may have good mechanical strength and effectively suppress growth oflithium dendrites.

The ion conductive polymer 14 may include any material that is capableof acting as a binder for aiding the adhesion of the particles 13 of theprotective layer 12 to an upper surface of the lithium metal electrode11, and may improve the mechanical strength of the protective layer 13.For example, the ion conductive polymer 14 may include any polymerhaving ion conductive characteristics suitable for use in a lithiummetal batteries. The ion conductive polymer 14 includes, for example, ahomopolymer, a copolymer, and a cross-linked polymer.

The copolymer as the ion conductive polymer 14 may be a block copolymer,a random copolymer, a graft copolymer, or an alternating copolymer. Acombination comprising at least one of the foregoing may also be used.

The cross-linked polymer as the ion conductive polymer 14 may be anypolymer having bond which links one polymer chain to another, forexample, a polymer prepared by cross-linking of cross-linkablefunctional groups. The cross-linked polymer as the ion conductivepolymer 14 may be a cross-linked product of a copolymer including across-linkable functional group as a repeating unit.

The cross-linked polymer as the ion conductive polymer 14 may be across-linked product of a block copolymer including a polystyrene blockand a polyethylene oxide block having an acrylate functional group; or across-linked product of a compound including a (C₁-C₉ alkyl)(meth)acrylate, C₁-C₉ alkenyl acrylates, a (C₁-C₁₂ glycol) diacrylate, apoly(C₂-C₆ alkylene glycol) diacrylate, a poly(C₂-C₉ glycol)polyacrylate, or a combination thereof. Examples of the (C₁-C₉ alkyl)(meth)acrylates include hexyl acrylate, or 2-ethylhexyl acrylate, andexamples of the C₁-C₉ alkenyl acrylates includes, allyl methacrylate.

Examples of the glycol diacrylates include 1,4-butanediol diacrylate,1,3-butylene glycol diacrylate, 1,6-hexanediol diacrylate, ethyleneglycol diacrylate, neopentyl glycol diacrylate, or a combinationthereof. Examples of the polyalkylene glycol diacrylates includediethylene glycol diacrylate, triethylene glycol diacrylate,tetraethylene diacrylate, tripropylene glycol diacrylate, polyethyleneglycol diacrylate, polypropyleneglycol acrylate, or a combinationthereof.

Examples of the polyol polyacrylates include trimethylol propanetriacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate,or a combination thereof.

The ion conductive polymer 14 may include polystyrene, a block copolymerincluding a styrene repeating unit, or a combination thereof. Forexample, the ion conductive polymer 14 may be at least one selected frompolystyrene, a poly(styrene-divinylbenzene) block copolymer, apoly(styrene-isoprene) block copolymer, a poly(styrene-isoprene-styrene)block copolymer, a poly(styrene-butadiene) block copolymer, apoly(styrene-butadiene-styrene) block copolymer, apoly(styrene-ethylene-butylene-styrene) block copolymer, apoly(styrene-methyl methacrylate) block copolymer, apoly(styrene-acrylonitrile) block copolymer, apoly(styrene-vinylpyridine) block copolymer,poly(acrylonitrile-butadiene-styrene) copolymer, apoly(acrylonitrile-ethylene-propylene-styrene) copolymer, a poly(methylmethacrylate-acrylonitrile-butadiene-styrene) copolymer, a poly((C₁-C₉alkyl) methacrylate-butadiene-styrene) copolymer, a poly(styrene-(C₁-C₉alkyl) acrylate) copolymer, a poly(acrylonitrile-styrene-(C₁-C₉ alkyl)acrylate) copolymer, or a combination thereof.

For example, the poly(styrene-divinylbenzene) copolymer may berepresented by Formula 1.

In Formula 1, a and b as mole fractions are each independently 0.01 to0.99, wherein the sum of a and b is equal to 1. In Formula 1, a may befrom 0.95 to 0.99, or 0.96 to 0.99, or for example, from 0.98 to 0.99;and b may be from 0.01 to 0.05, or 0.01 to 0.04, or for example, from0.01 to 0.02.

For example, the poly(styrene-divinylbenzene) copolymer may berepresented by Formula 1a.

For example, the poly(styrene-divinylbenzene) copolymer may berepresented by Formula 1b.

The poly(acrylonitrile-butadene-styrene) copolymer may be represented byFormula 2.

In Formula 2, x, y, and z as mole fractions are each independently from0.01 to 0.99, wherein the sum of x, y, and z is equal to 1.

In Formula 2, x may be from 0.1 to 0.35, y may be from 0.05 to 0.55, andz may be from 0.2 to 0.7. For example, x may be from 0.15 to 0.35, y maybe from 0.05 to 0.3, and z may be from 0.4 to 0.6.

The poly(styrene-divinylbenzene) copolymer represented by Formula 1 andthe poly(acrylonitrile-butadiene-styrene) copolymer represented byFormula 2 may each independently have a degree of polymerization ofabout 2 to about 5,000, or about 3 to about 2,000, or for example, about5 to about 1,000.

For example, the poly(styrene-divinylbenzene) copolymer represented byFormula 1 and the poly(acrylonitrile-butadiene-styrene) copolymerrepresented by Formula 2 may be a block copolymer.

In some embodiments, the protective layer 12 may have a single layerstructure of the particles 13, as illustrated in FIGS. 1A and 1B.

In some other embodiments, the protective layer 12 may have a doublelayer structure in which the particles 13 are stacked as a double layeron the lithium metal electrode 11, as illustrated in FIG. 1C. Theparticles 13 stacked as a double layer may also be surrounded by the ionconductive polymer 14, as illustrated in FIG. 1B.

In some other embodiments, the protective layer 12 may have a multilayerstructure in which particles 13 a, 13 b, and 13 c having different sizesmay be mixed together, as illustrated in FIG. 1D. When the protectivelayer 12 has such a multilayer structure in which the particles 13 a, 13b, and 13 c having different sizes are mixed together, the space fordendritic growth may be suppressed by lowering the porosity or improvingthe packing density of the protective layer 12, and thereby minimizingcontact between the electrolyte and the lithium metal. The dendriticgrowth may also be suppressed by increasing the thickness of theprotective layer 12.

The particles 13 in the protective layer 12 may include, for example, apoly(styrene-divinylbenzene) copolymer. When the particles 13 in theprotective layer 12 are formed of a cross-linked polymer as describedabove, the particles 13 may be chemically linked to one another, andthus form a high-intensity microsphere network structure.

The protective layer 12 may have a porosity of about 25 to about 50%,for example, about 28% to about 48%, or about 30 to about 45%. A poresize and porosity of the protective layer 12 may be determined dependingon the size of the particles 13.

In the protective layer 12 according to any of the above-describedembodiments, substantially no agglomeration of the particles 13 occurs,so that the protective layer 12 may have a uniform thickness. Theprotective layer 12 may have a thickness of about 1 μm to about 10 μm,for example about 2 μm to about 9 μm, or for example, about 3 to about 8μm. A thickness deviation of the protective layer 12 may be from about0.1 to about 4 μm, and in some embodiments, about 0.1 to about 3 μm, andin some other embodiments, about 0.1 μm to about 2 μm.

The protective layer further includes a liquid electrolyte. The liquidelectrolyte includes a lithium salt and an organic solvent. The lithiumsalt of the liquid electrolyte in the protective layer 12 may include,for example, LiSCN, LiN(CN)₂, LiCIO₄, LiBF₄, LiAsF₆, LiPF₆, LiCF₃SO₃,LiC(CF₃SO₂)₃, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)², LiN(SO₂F)₂, LiSbF₆,LiPF₃(CF₂CF₃)₃, LiPF₃(CF₃)₃, LiB(C₂O₄)₂, or a combination thereof.

The amount of the lithium salt in the protective layer 12 may be fromabout 10 to about 70 parts by weight, or about 15 to 60 parts by weight,and in some embodiments, about 20 to about 50 parts by weight, based on100 parts by weight of the particles 13. When the amount of the lithiumsalt is within these ranges, the protective layer 12 may have good ionconductivity.

The organic solvent of the liquid electrolyte in the protective layer 12may be a carbonate compound, a glyme compound, and a dioxolane compound.For example, the carbonate compound may be ethylene carbonate, propylenecarbonate, dimethyl carbonate, fluoroethylene carbonate, diethylcarbonate, or ethyl methyl carbonate. A combination comprising at leastone of the foregoing may also be used.

The glyme compound may be, for example, poly(ethylene glycol)dimethylether (PEGDME; polyglyme), tetra(ethylene glycol)dimethyl ether (TEGDME;tetraglyme), tri(ethylene glycol)dimethyl ether (triglyme),poly(ethylene glycol)dilaurate (PEGDL), poly(ethyleneglycol)monoacrylate (PEGMA), poly(ethylene glycol)diacrylate (PEGDA), ora combination thereof.

The dioxolane compound may be, for example, 1,3-dioxolane,4,5-diethyl-1,3-dioxolane, 4,5-dimethyl-1,3-dioxolane,4-methyl-1,3-dioxolane, and 4-ethyl-1,3-dioxolane. For example, theorganic solvent may be 2,2-dimethoxy-2-phenyl acetophenone,dimethylether (DME), 1,2-dimethoxyethane, 1,2-diethoxyethane,tetrahydrofuran, gamma-butyrolactone, 1,1,2,2-tetrafluoroethyl2,2,3,3-tetrafluoropropyl ether, or the like, or a combination thereof.

For example, the organic solvent may be ethylene carbonate, propylenecarbonate, dimethyl carbonate, diethyl carbonate, ethyl methylcarbonate, fluoroethylene carbonate, gamma-butyrolactone,1,2-dimethoxyethane, 12-diethoxyethane, dimethylene glycol dimethylether, trimethylene glycol dimethyl ether, tetramethylene glycoldimethyl ether, polyethylene glycol dimethyl ether, succinonitrile,sulfolane, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone,adiponitrile, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether,or a combination thereof.

FIGS. 1E and 1F are schematic views for explaining the effects of alithium negative electrode according to an embodiment.

Referring to FIG. 1E, a lithium negative electrode according to anembodiment may have a structure including a protective layer 12 on alithium metal electrode 11 that has a solid-electrolyte interphase (SEI)15 thereon, the protective layer 12 including particles 13. The lithiummetal electrode 11 and the SEI 15 may have soft characteristics due to,for example, a small thickness thereof, and thus may be pressed down bythe particles 13, resulting in the formation of grooves in the lithiummetal electrode 11 and the SEI 15.

In FIG. 1E, the particles 13 may include, for example, cross-linkedpolystyrene microspheres. Without being limited by theory, it isbelieved that the pressing force exerted by the particles 13 on thelithium metal electrode 11 and the SEI 15, may suppress lithiumdendritic growth and guide growth of lithium dendrites into the gaps(spaces) between the particles 13. When a negative electrode includingsuch a protective layer as illustrated in FIG. 1E is charged, lithiumdeposition may occur to form a lithium deposition layer 16 on thelithium metal electrode 11, as illustrated in FIG. 1F, with the SEI 15and the protective layer 12 including the particles 13 being stacked inthe stated order on the lithium deposition layer 16.

When using the protective layer 12, the lithium deposition density ofthe negative electrode may be remarkably improved as compared to anegative electrode which does not include the protective layer. Inaddition, the network and pore structures of the protective layer 12 mayserve as spaces for dendritic growth and at the same time control theamount of dendritic growth, and finally may adsorb byproducts from apositive electrode. Thus, a lithium metal battery including such alithium negative electrode according to any of the above-describedembodiments, may have improved lifetime and high-temperature stability.

In some embodiments, a lithium metal battery using a negative electrodeaccording to any of the above-described embodiments may have a lithiumdeposition density of about 0.2 to 0.3 grams per cubic centimeter(g/cm³, g/cc), for example, about 0.209 to about 0.29 g/cm³, or forexample, about 0.201 to 0.280 g/cm³, on the surface of the lithium metalelectrode when charged.

In some embodiments, a lithium metal battery including a lithiumnegative electrode according to any of the above-described embodimentsmay have a lithium deposition density which is greater than a lithiumdeposition density of a lithium metal battery which does not include theprotective layer (i.e., a lithium metal battery using bare lithium metalas a negative electrode). The lithium negative electrode may have alithium deposition density which is at least about 50% or greater, or55% or greater, or 58% or greater, or for example, about 50% to about75% greater, or about 50 to 60% greater, with respect to a lithium metalbattery using bare lithium metal as a negative electrode. Thisremarkable improvement in lithium deposition density is attributed tothe protective layer 12 having high strength in the negative electrode.The protective layer may have a Young's modulus of about 10⁶ Pa orgreater, for example, about 6 to 8 gigapascals (GPa), as measured atabout 25° C.

When the protective layer has a Young's modulus within these ranges, theprotective layer may effectively suppress volume change in the negativeelectrode, and the negative electrode may less likely to be partiallybroken by the formation of lithium dendrites on the surface of thelithium metal electrode and cause a short.

In some embodiments, the protective layer may have a tensile strength ofabout 2 megapascals (MPa) or greater, or about 5 MPa or greater, orabout 10 MPa or greater, as measured at about 25° C. An interfacialresistance between the lithium metal electrode and the protective layer,which may be obtained through an impedance measurement and using aNyquist plot, may be decreased by at least about 10%, as measured atabout 25° C., compared to bare lithium metal. The negative electrodeaccording to any of the above-described embodiments including theprotective layer for the lithium metal electrode may have lowerinterfacial resistance and thus better interfacial characteristics, ascompared to a lithium metal electrode not including a protective layer.For example, the negative electrode may have an oxidation current orreduction current of about 0.05 milliAmpere per square centimeter(mA/cm²) or less in a voltage range of about 0.0 volts (V) to about 6.0V with respect to lithium metal.

When using a protective layer according to any of the above-describedembodiments, a lithium metal battery may be substantially free ofbattery swelling issues after repeated cycles of charging anddischarging.

In some embodiments, the direct contact region between the liquidelectrolyte in the protective layer and the lithium metal electrode maybe about 30 to 50 volume % based on a total volume of the direct contactregion between the protective layer and the lithium metal electrode.

FIGS. 9A to 9C are schematic views of negative electrodes for lithiummetal batteries, according to embodiments, illustrating the arrangementof microspheres on an upper surface of a lithium metal electrode 11.

Referring to FIGS. 9A, 9B, and 9C, microspheres 13 having a diameter ofabout 3 μm may be disposed on the upper surface of the lithium metalelectrode 11. In FIGS. 9A to 9B, the microspheres 13 are on the uppersurface of the lithium metal electrode 11.

In the embodiments of FIGS. 9A to 9C, the lithium metal electrode 11 mayhave a length of about 5.4 μm.

26 In FIGS. 9A, 9B, and 9C, a, which indicates a buried depth of themicrospheres 13, is about 1.2 μm, 0.9 μm, and 0.5 μm in the negativeelectrodes of FIGS. 9A, 9B, and 9C, respectively. The direct contactregion between liquid electrolyte in the protective layer and thelithium metal electrode may be about 33.3 volume percent (vol %), 50 vol% and 72.2 vol %, based on a total volume of the direct contact regionbetween the protective layer and the lithium metal electrode in theembodiments of FIGS. 9A, 9B, and 9C, respectively.

A method of manufacturing a negative electrode for a lithium metalbattery, according to an embodiment, may be as follows.

First, particles having a size greater than 1 μm and about 100 μm aremixed with a solvent to prepare a protective layer-forming composition.

The protective layer-forming composition may be coated on a lithiummetal electrode and dried to form a protective layer, therebymanufacturing the negative electrode for a lithium metal battery.

The solvent may be, for example, tetrahydrofuran, N-methylpyrrolidone,or the like. The amount of the solvent may be from about 100 parts to5,000 parts by weight based on 100 parts by weight of the particles.

An ion conductive polymer may be further added to the protectivelayer-forming composition.

At least one selected from an ionic liquid, a polymer ionic liquid(PIL), and a lithium salt may be further added to the protectivelayer-forming composition.

The coating may be performed using any method suitable for forming aprotective layer, for example, spin coating, roll coating, curtaincoating, extruding, casting, screen printing, inkjet printing, doctorblade coating, or the like.

The drying may be performed at a temperature of about 20 to 25° C. Whenthe drying is performed at a low temperature within this temperaturerange, deformation of the lithium metal electrode may not occur. Aprotective layer having a monodisperse single layer structure may beformed through direct coating of the protective layer-formingcomposition on the lithium metal electrode, thereby improving efficiencyin protective layer formation process. The resulting protective layermay also have good mechanical strength and improved ion conductivity.

The drying may be followed by roll-pressing. This roll-pressing may beperformed under the conditions which are suitable roll-pressingconditions for manufacturing batteries in the art. The roll-pressing maybe performed, for example, at a pressure of about 1 kilogram force percentimeter (kgf/cm) to about 1.5 kgf/cm.

The protective layer may have an oxidation current or reduction currentof about 0.05 mA/cm² or less in a voltage range of about 0.0V to 6.0Vwith respect to lithium metal. The protective layer may beelectrochemically stable in a voltage range of about 0V to 6.0V, and insome embodiments, about 0V to 5.0V, and in some other embodiments, about0V to 4.0V, with respect to lithium. In some embodiments, the protectivelayer may have an electrochemically stable wide voltage window, and thusmay be applicable to an electrochemical device operating at a highvoltage.

The at least one particle in the protective layer may be an organicparticle. The organic particle may include, for example, polystyrene, apoly(styrene-divinylbenzene) copolymer, or a combination thereof.

The at least one particle in the protective layer may be an inorganicparticle. The inorganic particle may include, for example, SiO₂, TiO₂,ZnO, Al₂O₃, BaTiO₃, or a combination thereof.

The at least one particle in the protective layer may be anorganic-inorganic particle. The organic-inorganic particle may include,for example, a cage-structured silsesquioxane, a metal-organic framework(MOF), or a combination thereof.

For example, the cage-structured silsesquioxane may be a polyhedraloligomeric silsesquioxane (POSS). The number of silicon atoms in thePOSS may be about 8 or less, for example, 6, 7, or 8. For example, thecage-structured silsesquioxane may be a compound represented by Formula3.

Si_(k)O_(1.5k)(R₁)_(a)(R₂)_(b)(R₃)_(c)  Formula 3

In Formula 3, R₁, R₂, and R₃ may be each independently a hydrogen, asubstituted or unsubstituted C1-C30 alkyl group, a substituted orunsubstituted C1-C30 alkoxy group, a substituted or unsubstituted C2-C30alkenyl group, a substituted or unsubstituted C2-C30 alkynyl group, asubstituted or unsubstituted C6-C30 aryl group, a substituted orunsubstituted C6-C30 aryloxy group, a substituted or unsubstitutedC2-C30 heteroaryl group, a substituted or unsubstituted C4-C30carbocyclic group, or a silicon-containing functional group.

In Formula 3, 0<a<20, 0<b<20, 0<c<20, and k=a+b+c, provided that a, b,and c are selected in such a way that 6≤k≤20.

The cage-structured silsesquioxane may be a compound represented byFormula 4 or a compound represented by Formula 5.

In Formula 4, R₁ to R₈ may be each independently a hydrogen, asubstituted or unsubstituted C1-C30 alkyl group, a substituted orunsubstituted C1-C30 alkoxy group, a substituted or unsubstituted C2-C30alkenyl group, a substituted or unsubstituted C2-C30 alkynyl group, asubstituted or unsubstituted C6-C30 aryl group, a substituted orunsubstituted C6-C30 aryloxy group, a substituted or unsubstitutedC2-C30 heteroaryl group, a substituted or unsubstituted C4-C30carbocyclic group, or a silicon-containing functional group.

In Formula 5, R₁ to R₆ may be each independently a hydrogen, asubstituted or unsubstituted C1-C30 alkyl group, a substituted orunsubstituted C1-C30 alkoxy group, a substituted or unsubstituted C2-C30alkenyl group, a substituted or unsubstituted C2-C30 alkynyl group, asubstituted or unsubstituted C6-C30 aryl group, a substituted orunsubstituted C6-C30 aryloxy group, a substituted or unsubstitutedC2-C30 heteroaryl group, a substituted or unsubstituted C4-C30carbocyclic group, or a silicon-containing functional group.

In some embodiments, R₁ to R₈ in Formula 4 and R₁ to R₆ in Formula 5each may be an isobutyl group. For example, the cage-structuredsilsesquioxane may be octaisobutyl-t8-silsesquioxane.

The MOF may be a porous crystalline compound in which a Group 2 to Group15 metal ion or a Group 2 to Group 15 metal ionic cluster is chemicallybonded with an organic ligand. The organic ligand refers to an organicgroup that may form an organic bond such as a coordinate bond, ionicbond, or covalent bond. For example, an organic group having at leasttwo binding sites for such metal ions as described above may form astable structure through binding with the metal ions.

The Group 2 to Group 15 metal ion may include cobalt (Co), nickel (Ni),molybdenum (Mo), tungsten (W), ruthenium (Ru), osmium (Os), cadmium(Cd), beryllium (Be), calcium (Ca), barium (Ba), strontium (Sr), iron(Fe), manganese (Mn), chromium (Cr), vanadium (V), aluminum (Al),titanium (Ti), zirconium (Zr), copper (Cu), zinc (Zn), magnesium (Mg),hafnium (Hf), niobium (Nb), tantalum (Ta), rhenium (Re), rhodium (Rh),iridium (Ir), palladium (Pd), platinum (Pt), silver (Ag), scandium (Sc),yttrium (Y), indium (In), thallium (TI), silicon (Si), germanium (Ge),tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), or acombination thereof. The organic ligand may be a group derived from acompound including an aromatic dicarboxylic acid, an aromatictricarboxylic acid, an imidazole-based compound, a tetrazole,1,2,3-triazole, 1,2,4-triazole, pyrazole, an aromatic sulfonic acid, anaromatic phosphoric acid, an aromatic sulfinic acid, an aromaticphosphinic acid, a bipyridine, or a compound having a functional groupincluding an amino group, an imino group, an amide group, a dithiocarboxylic acid group (—CS₂H), a dithio carboxylate group (—CS₂ ⁻), apyridine group, or a pyrazine group, or a combination thereof. Acombination comprising at least one of the foregoing may also be used.

Non-limiting examples of the aromatic dicarboxylic acid and aromatictricarboxylic acid are benzene dicarboxylic acid, benzene tricarboxylicacid, biphenyl dicarboxylic acid, and terphenyl-dicarboxylic acid.

For example, the organic ligand may be a group originating fromcompounds represented by Formula 6.

The MOF may be, for example, Ti₈O₈(OH)₄[O₂C—C₆H₄—CO₂]₆, Cu(bpy)(H₂O)₂(BF₄)₂(bpy) {bpy=4,4′-bipyridine}, Zn₄O(O₂C—C₆H₄—CO₂)₃(Zn-terephthalic acid-MOF, Zn-MOF), or A(OH){O₂C—C₆H₄—CO₂}.

The protective layer may include i) a particle A including acage-structured silsesquioxane, an MOF compound,Li_(1+x+y)Al_(x)Ti_(2−x)Si_(y)P_(3−y)O₁₂ (wherein 0<x<2 and 0≤y<3),BaTiO₃, Pb(Zr_(p)Ti_(1−p))O₃ wherein 0≤p≤1 (PZT),Pb_(1−x)La_(x)Zr_(1−y)Ti_(y)O₃ (PLZT, wherein 0≤x<1 and 0≤y<1),Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN-PT), HfO₂, SrTiO₃, SnO₂, CeO₂, Na₂O,MgO, NiO, CaO, BaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, TiO₂, SiO₂, SiC, lithiumphosphate (Li₃PO₄), Li_(x)Ti_(y)(PO₄)₃ (lithium titanium phosphate,wherein 0<x<2 and 0<y<3), Li_(x)Al_(y)Ti_(z)(PO₄)₃ (lithium aluminumtitanium phosphate, wherein 0<x<2, 0<y<1, and 0<z<3), Li_(1+x+y)(Al,Ga)_(x)(Ti, Ge)_(2−x)Si_(y)P_(3−y)O₁₂ (wherein 0≤x≤1 and 0≤y≤1),Li_(x)La_(y)TiO₃ (lithium lanthanum titanate, wherein 0≤x<2 and 0<y<3),Li_(x)Ge_(y)P_(z)S_(w) (lithium germanium thiophosphate, wherein 0≤x<4,0<y<1, 0<z<1, and 0<w<5), Li_(X)N_(y) (lithium nitride, wherein 0<x<4and 0<y<2), Li_(X)Si_(y)S_(z) (SiS2 glass, wherein 0≤x<3, 0<y<2, and0<z<4), Li_(x)P_(y)S_(z) (P₂S₅ glass, wherein 0≤x<3, 0<y<3, and 0<z<7),Li₂O, LiF, LiGH, Li₂CO₃, LiAlO₂, Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂—GeO₂, andLi_(3+x)La₃M₂O₁₂ (wherein 0≤x≤5, and M is Te, Nb, or Zr); ii) across-linked product of a particle A having cross-linkable functionalgroups; or a combination thereof.

The cross-linkable functional group may be any cross-linkable functionalgroup, for example, an acrylate group, a methacrylate group, an epoxygroup, or the like, or a combination thereof.

When the at least one particle in the protective layer has across-linkable functional group on a surface thereof, the particles maybe covalently linked so that the protective layer may have improvedmechanical strength.

The ionic liquid which may be added to the protective layer-formingcomposition refers to a salt in a liquid state at room temperature or afused salt at room temperature that consists of ions having a meltingpoint equal to or below room temperature. The ionic liquid may be acompound including: i) a cation including an ammonium cation, apyrrolidinium cation, a pyridinium cation, a pyrimidinium cation, animidazolium cation, a piperidinum cation, a pyrazolium cation, anoxazolium cation, a pyridazinium cation, a phosphonium cation, asulfonium cation, a triazolium cation, or a combination thereof, and ii)an anion including BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻, ClO₄⁻, CH₃SO₃ ⁻, CF₃CO₂ ⁻, Cl⁻, Br⁻, I⁻, BF₄ ⁻, SO₄ ²⁻, CF₃SO₃ ⁻, (FSO₂)₂N⁻,(C₂F₅SO₂)₂N⁻, (C₂F₅SO₂)(CF₃SO₂)N⁻, (CF₃SO₂)₂N⁻, or a combinationthereof.

In some embodiments, the ionic liquid may includeN-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide,N-butyl-N-methyl-pyrrolidinium bis(3-trifluoromethylsulfonyl)imide,1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide,1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, or acombination thereof.

The amount of the ionic liquid may be from about 5 parts by weight toabout 40 parts by weight, or from about 7.5 parts by weight to about 30parts by weight, and in some embodiments, about 10 parts by weight toabout 20 parts by weight, based on 100 parts by weight of the particlesin the protective layer. When the amount of the ionic liquid is withinthese ranges, the protective layer may have improved ion conductivityand improved mechanical properties.

When the protective layer includes an ionic liquid (IL) and a lithiumsalt, the mole ratio (IL/Li) of the ionic liquid to lithium ions may beabout 0.1 to 2.0, and in some embodiments, about 0.2 to 1.8, and in someother embodiments, about 0.4 to 1.5. When the mole ratio of the ionicliquid to lithium ions is within these ranges, the protective layer mayhave high lithium ion mobility, high ion conductivity, and improvedmechanical properties to effectively suppress growth of lithium dendriteon a surface of the negative electrode.

The polymer ionic liquid which may be added to the protectivelayer-forming composition may be, for example, a polymerization productof ionic liquid monomers, or a polymeric compound. The polymer ionicliquid is highly dissoluble in an organic solvent, and thus may furtherimprove the ion conductivity of a polymer layer when added to theprotective layer-forming composition.

When the polymer ionic liquid is prepared by polymerization of ionicliquid monomers as described above, a resulting product from thepolymerization reaction may be washed and dried, followed by an anionicsubstitution reaction to have appropriate anions that may improvesolubility in an organic solvent

In some embodiments, the polymer ionic liquid may include a repeatingunit that includes: i) a cation including an ammonium cation, apyrrolidinium cation, a pyridinium cation, a pyrimidinium cation, animidazolium cation, a piperidinum cation, a pyrazolium cation, anoxazolium cation, a pyridazinium cation, a phosphonium cation, asulfonium cation, a triazolium cation, or a combination thereof, and ii)an anion including BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻, ClO₄⁻, CH₃SO₃ ⁻, CF₃CO₂ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻, Cl⁻, Br⁻, I⁻, SO₄ ²⁻,CF₃SO₃ ⁻, (C₂F₅SO₂)₂N⁻, (C₂F₅SO₂)(CF₃SO₂)N—, NO₃ ⁻, Al₂Cl₇, (CF₃SO₂)₃C⁻,(CF₃)₂PF₄, (CF₃)₃PF₃, (CF₃)₄PF₂, (CF₃)₅PF⁻, (CF₃)₆P⁻, SF₅CF₂SO₃ ⁻,SF₅CHFCF₂SO₃ ⁻, CF₃CF₂(CF₃)₂CO⁻, (CF₃SO₂)₂CH⁻, (SF₅)₃C⁻,(O(CF₃)₂C₂(CF₃)₂O)₂PO⁻, or a combination thereof.

In some embodiments, the polymer ionic liquid may be prepared bypolymerization of ionic liquid monomers. For example, the ionic liquidmonomers may have a polymerizable functional group such as a vinylgroup, an allyl group, an acrylate group, or a methacrylate group, andmay include a cation including an ammonium cation, a pyrrolidiniumcation, a pyridinium cation, a pyrimidinium cation, an imidazoliumcation, a piperidinum cation, a pyrazolium cation, an oxazolium cation,a pyridazinium cation, a phosphonium cation, a sulfonium cation, atriazolium cation, or a combination thereof, and at least one of theabove-listed anions.

Non-limiting examples of the ionic liquid monomers are1-vinyl-3-ethylimidazolium bromide, a compound represented by Formula 7,or a compound represented by Formula 8.

For example, the polymer ionic liquid may be a compound represented byFormula 9 or a compound represented by Formula 10.

In Formula 9, R₁ and R₃ may be each independently a hydrogen, asubstituted or unsubstituted C1-C30 alkyl group, a substituted orunsubstituted C2-C30 alkenyl group, a substituted or unsubstitutedC2-C30 alkynyl group, a substituted or unsubstituted C6-C30 aryl group,a substituted or unsubstituted C2-C30 heteroaryl group, or a substitutedor unsubstituted C4-C30 carbocyclic group; R₂ may be a chemical bond, aC1-C30 alkylene group, a C6-C30 arylene group, a C2-C30 heteroarylenegroup, or a C4-C30 divalent carbocyclic group; X⁻ indicates an anion ofthe ionic liquid; and n may be from about 500 to 2800.

In Formula 10, Y⁻ may be an anion of the ionic liquid 9; and n may be500 to 2800.

For example, in Formula 10, Y⁻ may be bis(trifuoromethylsulfonyl)imide(TFSI), bis(fluorosulfonyl)imide, BF₄, or CF₃SO₃.

The polymeric ionic liquid may include, for example a cation includingpoly(1-vinyl-3-alkylimidazolium), poly(1-allyl-3-alkylimidazolium), orpoly(1-(methacryloyloxy-3-alkylimidazolium), and an anion includingCH₃COO⁻, CF₃COO⁻, CH₃SO₃ ⁻, CF₃SO₃ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻,(CF₃SO₂)₃C⁻, (CF₃CF₂SO₂)₂N⁻, C₄F₉SO₃ ⁻, C₃F₇COO⁻, or (CF₃SO₂)(CF₃CO)N⁻.

For example, the compound of Formula 10 may be poly(diallyldimethylammonium bis(trifluoromethylsulfonyl)imide).

In some embodiments, the polymer ionic liquid may include alow-molecular weight polymer, a thermally stable ionic liquid, and alithium salt. The low-molecular weight polymer may have an ethyleneoxide chain. The low-molecular weight polymer may be a glyme.Non-limiting examples of the glyme are polyethyleneglycol dimethylether(polyglyme), tetraethyleneglycol dimethyl ether (tetraglyme), andtriethyleneglycol dimethylether (triglyme).

The low-molecular weight polymer may have a weight average molecularweight of about 75 to about 2000 Daltons, or about 100 to about 1000Daltons, or for example, a weight average molecular weight of about 250to about 500 Daltons. The thermally stable ionic liquid may be the sameas those listed above in conjunction with the above-described ionicliquid.

The protective layer may further include an oligomer. For example, theoligomer in the protective layer may include polyethylene glycoldimethyl ether, polyethylene glycol diethyl ether, or a combinationthereof. The oligomer may have a weight average molecular weight ofabout 200 to about 2,000 Daltons, or about 300 to about 1800 Daltons, orabout 400 to about 1500 Daltons. The amount of the oligomer may be about5 parts by weight to about 50 parts by weight, or about 10 parts byweight to about 40 parts by weight, or about 10 parts by weight to about30 parts by weight, based on 100 parts by weight of the particles in theprotective layer. When such an oligomer is added, the protective layermay have further improved film formability, mechanical properties, andion conductivity characteristics.

The protective layer may have an ion conductivity as measured at about25° C. of about 1×10⁻⁴ Siemens per centimeter (S/cm) or greater, and insome embodiments, about 5×10⁻⁴ S/cm or greater, and in some otherembodiments, about 1×10⁻³ S/cm or greater.

The protective layer of the negative electrode according to any of theabove-described embodiments may be applicable to a lithium metalbattery, for example, a lithium air battery, a lithium ion battery, or alithium polymer battery, or the like.

In some embodiments, the protective layer may be suitable as aprotective layer for a high-voltage lithium secondary battery. The term“high-voltage” refers to a charging voltage of about 4.0 V to 5.5 V.

According to another embodiment of the present disclosure, there isprovided a lithium metal battery including a positive electrode, thenegative electrode according to any of the above-described embodiments,and an electrolyte between the positive and negative electrodes.

The electrolyte may include a liquid electrolyte, a solid electrolyte, agel electrolyte, a polymer ionic liquid, or a combination thereof. Forexample, the electrolyte may be a mixed electrolyte including at leastone of these electrolytes. The lithium metal battery may further includea separator.

The at least one selected from a liquid electrolyte, a polymeric ionicliquid, a gel electrolyte, and a solid electrolyte may be between thepositive electrode and the electrolyte. The gel electrolyte may be anygel electrolyte known in the art. For example, the gel electrolyte mayinclude a polymer and a polymer ionic liquid. For example, the polymermay be a solid graft (block) copolymer electrolyte.

The solid electrolyte may be, for example, an organic solid electrolyteor an inorganic solid electrolyte. Non-limiting examples of the organicsolid electrolyte are polyethylene derivatives, polyethylene oxidederivatives, polypropylene oxide derivatives, phosphoric acid esterpolymer, polyester sulfide, polyvinyl alcohol, polyfluoride vinylidene,and polymers including ionic dissociative groups. A combinationcomprising at least one of the foregoing may also be used.

Non-limiting examples of the inorganic solid electrolyte are Li₃N, LiI,Li₅NI₂, Li₃N—LiI—LiOH, Li₂SiS₃, Li₄SiO₄, Li₄SiO₄—LiI—LiOH,Li₃PO₄—Li₂S—SiS₂, Cu₃N, LiPON, Li₂S.GeS₂.Ga₂S₃, Li₂O.11Al₂O₃,(Na,Li)_(1+x)Ti_(2−x)Al_(x)(PO₄)₃ (wherein 0.1≤x≤0.9),Li_(1+x)Hf_(2−x)Al_(x)(PO₄)₃ (wherein 0.1≤x≤0.9), Na₃Zr₂Si₂PO₁₂,Li₃Zr₂Si₂PO₁₂, Na₅ZrP₃O₁₂, Na₅TiP₃O₁₂, Na₃Fe₂P₃O₁₂, Na₄NbP₃O₁₂, sodiumsilicates, Li_(0.3)La_(0.5)TiO₃, Na₅MSi₄O₁₂ (wherein M is a rare earthelement, for example, Nd, Gd, Dy, or the like) Li₅ZrP₃O₁₂, Li₅TiP₃O₁₂,Li₃Fe₂P₃O₁₂, Li₄NbP₃O₁₂,Li_(1+x)(M,Al,Ga)_(x)(Ge_(1−y)Ti_(y))_(2−x)(PO₄)₃(wherein x≤0.8,0≤y≤1.0, and M is Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, or Yb),Li_(1+x+y)Q_(x)Ti_(2−x)Si_(y)P_(3−y)O₁₂ (wherein 0<x≤0.4, 0<y≤0.6, and Qis Al or Ga), Li₆BaLa₂Ta₂O₁₂, Li₇La₃Zr₂O₁₂, Li₅La₃Nb₂O₁₂, Li₅La₃M₂O₁₂(wherein M is Nb or Ta), and Li_(7+x)A_(x)La_(3−x)Zr₂O₁₂ (wherein 0<x<3and A is Zn). A combination comprising at least one of the foregoing mayalso be used.

In some embodiments, the protective layer of the negative electrode inthe lithium metal battery may include a metal salt containing a Group 1or Group 2 element and a nitrogen-containing additive; boron nitride; ora combination thereof.

The metal salt containing a Group 1 or Group 2 element may include Cs,Rb, K, Ba, Sr, Ca, Na, Mg, or a combination thereof. Thenitrogen-containing additive may include an inorganic nitrate, anorganic nitrate, an inorganic nitrite, an organic nitrite, an organicnitro compound, an organic nitroso compound, a N—O compound, a lithiumnitride (Li₃N), or a combination thereof.

The metal salt containing a Group 1 or Group 2 element and anitrogen-containing additive may be insoluble in an organic solvent of aliquid electrolyte of the electrolyte. Due to these insolublecharacteristics, the metal salt containing a Group 1 or Group 2 elementand a nitrogen-containing additive, when included in the protectivelayer, may be stably confined to a surface region of the lithium metalelectrode with limited mobility, so that migration of lithium ionsbetween electrodes may not be hindered.

The metal of the metal salt containing a Group 1 or Group 2 element hasa relatively larger atom size than lithium and thus may have a sterichindrance effect in the protective layer. Due to this steric hindrance,the metal salt containing a Group 1 or Group 2 element is able tosuppress growth of lithium dendrites on the surface of the lithium metalelectrode. A metal cation (for example, cesium (Cs) or rubidium (Rb)ions) in the metal salt containing a Group 1 or Group 2 element mayexhibit an effective reduction potential below the reduction potentialof lithium ions and thus may form a positively charged electrostaticshield around the initial growth tip of protuberances formed on thesurface of the lithium metal electrode without reduction or depositionof the metal salt during lithium deposition. The positively chargeelectrostatic shield may effectively suppress growth of lithiumdendrites on the surface of the lithium metal electrode. In order forthe metal salt containing a Group 1 or Group 2 element to have aneffective reduction potential below the reduction potential of lithiumions, as described above, the amount of the metal salt containing aGroup 1 or Group 2 is within a certain range. For example, the amount ofthe metal salt containing a Group 1 or Group 2 element may be controlledto be within a range of about 0.1 part by weight to about 100 parts byweight, or about 1 part by weight to about 75 parts by weight, or about10 parts by weight to about 50 parts by weight, based on 100 parts byweight of the particles in the protective layer.

The protective layer of the negative electrode in the lithium metalbattery may have good mechanical strength and flexibility to suppresslithium dendritic formation. The lithium metal battery may furtherinclude an ion-conductive thin film between the lithium metal electrodeand the protective layer. The ion-conductive thin film may improve theion conductivity of the protective layer and lithium ion mobility (orlithium ion transference number), and thus reduce an interfacialresistance between the lithium metal electrode and the protective layer.For example, the ion-conductive thin film may include lithium nitride(Li₃N).

The protective layer of the negative electrode in the lithium metalbattery may also chemically improve a deposition/dissolution process oflithium ions to thus thereby improve deposition morphology of thelithium metal electrode compared to when forming a conventionalprotective layer, and consequently increase deposition density on thesurface of the lithium metal electrode and lithium ion mobility (ortransference number). In addition, as described above, the metal saltcontaining a Group 1 or Group 2 element and a nitrogen-containingadditive is confined to the protective layer on the surface of thelithium metal electrode, and thus is unlikely to be dispersed in theliquid electrolyte or to migrate toward the positive electrode and reactwith the positive electrode. As a result, the lithium metal batteryincluding the protective layer may have improved rate capability andlifetime characteristics.

For example, the nitrogen-containing additive in the protective layermay include an inorganic nitrate, an organic nitrate, an inorganicnitrite, an organic nitrite, an organic nitro compound, an organicnitroso compound, a N—O compound, lithium nitride (Li₃N), or acombination thereof. However, the nitrogen-containing additive is notlimited thereto.

For example, the inorganic nitrate may include lithium nitrate,potassium nitrate, cesium nitrate, barium nitrate, ammonium nitrate, ora combination thereof. For example, the organic nitrate may includedialkyl imidazolium nitrate, guanidine nitrate, ethyl nitrate, propylnitrate, butyl nitrate, pentyl nitrate, octyl nitrate, or a combinationthereof. For example, the organic nitrite may include ethyl nitrite,propyl nitrite, butyl nitrite, pentyl nitrite, octyl nitrite, or acombination thereof.

For example, the organic nitro compound may include nitromethane,nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitrotoluene,dinitrotoluene, nitropyridine, or a combination thereof. For example,the N—O compound may include pyridine N-oxide, alkylpyridine N-oxide,tetramethyl piperidine N-oxyl (TEMPO), or a combination thereof.

In an embodiment, the nitrogen-containing additive in the protectivelayer may comprise LiNO₃, Li₃N, or a combination thereof, and the Group1 element- or Group 2 element-containing metal salt in the protectivelayer may comprise cesium bis(trifluoromethylsulfonyl)imide (CsTFSI),CsNO₃, CsPF₆, CsFSI, CsAsF₆, CsClO₄, CsBF₄, or a combination thereof.For example, the metal salt containing a Group 1 or Group 2 element maybe CsTFSI.

The amount of the at least one of a metal salt containing a Group 1 orGroup 2 element and a nitrogen-containing additive in the protectivelayer may be from about 0.1 part by weight to about 100 parts by weight,or about 0.1 part by weight to about 50 parts by weight, and in someembodiments, about 0.1 part by weight to about 30 parts by weight, basedon 100 parts by weight of the particles in the protective layer. Whenthe amount of the at least one of a metal salt containing a Group 1 orGroup 2 element and a nitrogen-containing additive is within any ofthese ranges, the lithium metal battery may have a lithium dendriticgrowth suppression effect, a reduced interfacial resistance between thesurface of the lithium metal electrode and the protective layer, andimproved lithium ion mobility.

In some embodiments, the protective layer may include only a metal saltcontaining a Group 1 or Group 2 element. In this regard, the amount ofthe metal salt containing a Group 1 or Group 2 element may be about 0.1part by weight to about 100 parts by weight, or about 0.1 part by weightto about 50 parts by weight, and in some embodiments, about 0.1 part byweight to about 30 parts by weight, based on 100 parts by weight of theparticles in the protective layer.

In some embodiments, the protective layer may include only anitrogen-containing additive. In this regard, the amount of thenitrogen-containing additive may be about 0.1 part by weight to about100 parts by weight, or about 0.1 part by weight to about 50 parts byweight, and in some embodiments, about 0.1 part by weight to about 30parts by weight, based on 100 parts by weight of the particles in theprotective layer.

In some other embodiments, the protective layer may include both a metalsalt containing a Group 1 or Group 2 element, and a nitrogen-containingadditive. In this regard, the amount of the metal salt containing aGroup 1 or Group 2 element may be about 0.01 part by weight to about99.99 parts by weight, and in some embodiments, about 0.05 part byweight to about 50 parts by weight, or about 0.1 part to about 30 partby weight, based on 100 parts by weight of the particles in theprotective layer. The amount of the nitrogen-containing additive may beabout 0.01 part by weight to about 99.99 parts by weight, or about 0.05part by weight to about 50 parts by weight, and in some embodiments,about 0.1 part to about 30 parts by weight, based on 100 parts by weightof the particles in the protective layer.

In some embodiments, a mixed weight ratio of the metal salt containing aGroup 1 or Group 2 element to the nitrogen-containing additive in theprotective layer may be about 1:9 to about 9:1, and in some otherembodiments, about 1:2 to about 2:1, and in some other embodiments,about 1:1. When the mixed weight ratio of the metal salt containing aGroup 1 or Group 2 element to the nitrogen-containing additive is withinany of these ranges, due to good deposition density on the surface ofthe lithium metal electrode and improved lithium ion mobilitycharacteristics in the electrolyte, the lithium metal battery may haveimproved rate capability and lifetime characteristics.

The lithium metal electrode of the negative electrode in the lithiummetal battery may be a lithium metal or a lithium metal alloy. Thelithium metal battery may further include a liquid electrolyte betweenthe negative electrode and the positive electrode, the liquidelectrolyte including at least one selected from an organic solvent, anionic liquid, and a lithium salt.

A lithium metal battery with improved capacity retention rate may bemanufactured using a negative electrode according to any of theabove-described embodiments. The lithium metal battery according to anyone of the above-described embodiments may have good voltagecharacteristics, high capacity, and high energy density, and thus may beused in a wide variety of applications including mobile phones, laptopcomputers, storage batteries for power generating units using wind poweror sunlight, electric vehicles, uninterruptable power supplies (UPS),household storage batteries, and the like.

FIGS. 1G to 1J are schematic views illustrating structures of lithiummetal batteries according to embodiments.

Referring to FIG. 1G, a lithium metal battery according to an embodimentmay have a structure including a positive electrode 21, a negativeelectrode 22 according to any of the above-described embodiments, and anelectrolyte 24 between the positive electrode 21 and the negativeelectrode 22. A protective layer 23 may be between the electrolyte 24and the negative electrode 22. The electrolyte 24 may include a liquidelectrolyte, a polymeric ionic liquid, a solid electrolyte, a gelelectrolyte, or a combination thereof. The lithium metal battery mayfurther include a separator.

The protective layer 23 may be disposed on at least a portion of thenegative electrode 22, so that the surface of the negative electrode 22may become mechanically and electrochemically stable. As a result,during charging and discharging the lithium metal battery, dendriticformation on the surface of the negative electrode 22 may be suppressed,and interfacial stability between the negative electrode 22 and theelectrolyte 24 may be improved. Thus, the lithium metal battery may haveimproved cycle characteristics.

The electrolyte 24 may have a two-layer stack structure including aliquid electrolyte 24 a and a solid electrolyte 24 b that may besequentially stacked, as illustrated in FIG. 1H. The liquid electrolyte24 a may be adjacent to the protective layer 23. The lithium metalbattery may have a stack structure of negative electrode/protectivelayer/electrolyte (liquid electrolyte/solid electrolyte)/positiveelectrode, in the stated order.

Referring to FIG. 1I, a lithium metal battery according to anotherembodiment may further include a separator 24 c. For example, theseparator may be a monolayer of polyethylene, polypropylene,polyvinylidene fluoride, or a combination thereof, or a multilayerincluding at least two layers of polyethylene, polypropylene,polyvinylidene fluoride, or a combination thereof. For example, theseparator may be a mixed multilayer structure, such as a two-layerseparator of polyethylene/polypropylene, a three-layer separator ofpolyethylene/polypropylene/polyethylene, or a three-layer separator ofpolypropylene/polyethylene/polypropylene. The separator may include anelectrolyte including a lithium salt and an organic solvent.

Referring to FIG. 1J, a lithium metal battery according to anotherembodiment may include a liquid electrolyte 24 a. The liquid electrolyte24 a may have a composition which is the same or different as thecomposition of the liquid electrolyte included in the protective layer23.

FIG. 1K is a schematic view illustrating a structure of a lithium metalbattery 30 according to another embodiment.

The lithium metal battery 30 may include a positive electrode 31, anegative electrode 32 according to any of the above-describedembodiments, and a battery case 34 accommodating the positiveelectrolyte 31 and the negative electrode 32.

In the embodiments of FIGS. 1G to 1K, the positive electrode 21 may be aporous positive electrode. The porous positive electrode may be apositive electrode including pores, or any positive electrode thatallows permeation of liquid electrolyte thereinto by capillary action.

For example, the porous positive electrode may be a positive electrodethat may be obtained by coating a cathode active material compositionincluding a positive active material, a conducting agent, a binder, anda solvent, and drying the resulting structure. The resulting positiveelectrode may include pores among particles of the positive activematerial. The porous positive electrode may be impregnated with liquidelectrolyte.

In some embodiments, the positive electrode may include a liquidelectrolyte, a gel electrolyte, or a solid electrolyte. The liquidelectrolyte, the gel electrolyte, and the solid electrolyte may be anyelectrolytes for lithium metal batteries that do not react with thepositive active material, and thus prevent deterioration of the positiveactive material during charging and discharging.

Each element of a lithium metal battery including a negative electrodeaccording to any of the embodiments, and a method of manufacturing thelithium metal battery now will be described in detail.

A positive active material for the positive electrode may includelithium cobalt oxide, lithium nickel cobalt manganese oxide, lithiumnickel cobalt aluminum oxide, lithium iron phosphate, lithium manganeseoxide, or a combination thereof, but is not limited thereto. Anysuitable positive active material may be used.

For example, the positive active material may be a compound representedby one of the following formulae: Li_(a)A_(1−b)B_(b)D₂ (wherein0.90≤a≤1.8, and 0≤b≤0.5); Li_(a)E_(1−b)B_(b)O_(2−c)D_(c) (wherein0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); LiE_(2−b)B_(b)O_(4−c)D_(c) (wherein0≤b≤0.5, and 0≤c≤0.05); Li_(a)Ni_(1−b−c)Co_(b)B_(c)D (wherein0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α≤2);Li_(a)Ni_(1−b−c)Co_(b)B_(c)O_(2−α)F_(α) (wherein 0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, and 0<α<2); Li_(a)Ni_(1−b−c)Mn_(b)B_(c)D_(α) (wherein0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<a≤2);Li_(a)Ni_(1−b−c)Mn_(b)B_(c)O_(2−α)F_(α) (wherein 0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, and 0<a<2); Li_(a)Ni_(b)E_(c)G_(d)O₂ (wherein 0.90≤a≤1.8,0≤b≤0.9, 0≤c≤0.5, and 0.001≤d≤0.1); Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂(wherein 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0.001≤e≤0.1);Li_(a)NiG_(b)O₂ (wherein 0.90≤a≤1.8, and 0.001≤b≤0.1); Li_(a)CoG_(b)O₂(wherein 0.90≤a≤1.8, and 0.001≤b≤0.1); Li_(a)MnG_(b)O₂ (wherein0.90≤a≤1.8, and 0.001≤b≤0.1); Li_(a)Mn₂GbO₄ (wherein 0.90≤a≤1.8, and0.001≤b≤0.1); QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₅; LiIO₂; LiNiVO₄;Li_((3−f))J₂(PO₄)₃ (wherein 0≤f≤2); Li_((3−f))Fe₂(PO₄)₃ (wherein 0≤f≤2);and LiFePO₄. A combination comprising at least one of the foregoing mayalso be used.

In the formulae above, A includes nickel (Ni), cobalt (Co), manganese(Mn), or a combination thereof; B includes aluminum (Al), nickel (Ni),cobalt (Co), manganese (Mn), chromium (Cr), iron (Fe), magnesium (Mg),strontium (Sr), vanadium (V), a rare earth element, or a combinationthereof; D includes oxygen (O), fluorine (F), sulfur (S), phosphorus(P), or a combination thereof; E includes cobalt (Co), manganese (Mn),or a combination thereof; F includes fluorine (F), sulfur (S),phosphorus (P), or a combination thereof; G includes aluminum (Al),chromium (Cr), manganese (Mn), iron (Fe), magnesium (Mg), lanthanum(La), cerium (Ce), strontium (Sr), vanadium (V), and combinationsthereof; Q is selected from the group consisting of titanium (Ti),molybdenum (Mo), manganese (Mn), or a combination thereof; I includeschromium (Cr), vanadium (V), iron (Fe), scandium (Sc), yttrium (Y), or acombination thereof; and J includes vanadium (V), chromium (Cr),manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), or a combinationthereof.

For example, the positive active material may be a compound representedby Formula 11, a compound represented by Formula 12, or a compoundrepresented by Formula 13.

Li_(a)Ni_(b)Co_(c)Mn_(d)O₂   Formula 11

In Formula 11, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, and 0≤d≤0.5.

Li₂MnO₃   Formula 12

LiMO₂   Formula 13

In Formula 13, M may be Mn, Fe, Co, or Ni.

The positive electrode of the lithium metal battery may be manufacturedas follows.

A positive active material, a binder, and a solvent are mixed to preparea positive active material composition. A conducting agent may befurther added into the positive active material composition. Thepositive active material composition is directly coated on a metalliccurrent collector and dried to prepare a positive electrode plate.Alternatively, the positive active material composition may be cast on aseparate support to form a positive active material film, which may thenbe separated from the support and laminated on a metallic currentcollector to prepare a positive electrode plate.

The binder is a composition that facilitates binding between an activematerial and a conductive material and binding with a current collector.Non-limiting examples of the binder include polyvinylidene fluoride(PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch,hydroxypropylcellulose, reproduced cellulose, polyvinylpyrrolidone,polytetrafluoroethylene, polyethylene, polypropylene,ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrenebutadiene rubber, fluorine rubber, and various copolymers. An amount ofthe binder added may be from about 1 part by weight to about 50 parts byweight based on 100 parts by weight, based on the total weight of thepositive active material. The amount of the binder may be from about 2parts by weight to about 5 parts by weight based on 100 parts by weightof the total weight of the positive active material. When the content ofthe binder is within this range, a binding force of the positive activematerial layer to the current collector may be satisfactory.

The conducting agent may be any material that does not cause a chemicalchange in the lithium metal battery and which has electricalconductivity. Non-limiting examples of the conducting agent includegraphite such as natural graphite or artificial graphite; carbonaceousmaterials, such as carbon black, acetylene black, Ketjen black, channelblack, furnace black, lamp black, or summer black; conductive fibers,such as carbon fibers or metal fibers; carbon fluoride; metal powder,such as aluminum or nickel powder; conductive whisky, such as zinc oxideor potassium titanate; a conductive metal oxide, such as a titaniumoxide; and a conductive material, such as a polyphenylene derivative. Acombination comprising at least one of the foregoing may also be used.

The amount of the conducting agent may be from about 1 part by weight toabout 10 parts by weight, for example, from about 2 parts by weight toabout 5 parts by weight, based on 100 parts by weight of the positiveactive material. When the amount of the conducting agent is within theseranges, the final positive electrode may have good conductivitycharacteristics.

A non-limiting example of the solvent is N-methylpyrrolidone.

The amount of the solvent may be from about 100 parts to about 2,000parts by weight based on 100 parts by weight of the positive activematerial. When the amount of the solvent is within this range, a processfor forming the positive active material layer may be easily carriedout.

The amounts of the positive active material, the conducting agent, thebinder, and the solvent may be determined by the person of skill in theart without undue experimentation. At least one of the conducting agent,the binder, and the solvent may be omitted depending on the use andstructure of a lithium metal battery.

The negative electrode may be, for example, a lithium metal thin film ora lithium metal alloy thin film, as described above.

A lithium metal alloy for the negative electrode may include lithium,and a metal/metalloid alloyable with lithium. Examples of themetal/metalloid alloyable with lithium are Si, Sn, Al, Ge, Pb, Bi, Sb, aSi—Y ally (wherein Y is an alkaline metal, an alkaline earth metal, aGroup 13 to Group 16 element, a transition metal, a rare earth element,or a combination thereof, except for Si), a Sn—Y alloy (wherein Y is analkaline metal, an alkaline earth metal, a Group 13 to Group 16 element,a transition metal, a rare earth element, or a combination thereof,except for Sn). Y may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V,Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd,Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te,Po, or a combination thereof.

The electrolyte may include a separator and/or a lithium salt-containingnonaqueous electrolyte which are suitable for use in lithium metalbatteries in the art.

The separator may be an insulating thin film having high ionpermeability and high mechanical strength. The separator may have a porediameter of about 0.01 μm to about 10 μm, and a thickness of about 5 μmto about 20 μm. Non-limiting examples of the separator are olefin-basedpolymers, such as polypropylene, and sheets or non-woven fabric made ofglass fiber or polyethylene. When a lithium metal battery contains asolid polymer electrolyte, the solid polymer electrolyte may also serveas the separator.

For example, the separator may be a monolayer or a multilayer includingat least two layers of polyethylene, polypropylene, polyvinylidenefluoride, or a combination thereof. For example, the separator may be amixed multilayer, such as a two-layer separator ofpolyethylene/polypropylene, a three-layer separator ofpolyethylene/polypropylene/polyethylene, or a three-layer separator ofpolypropylene/polyethylene/polypropylene. The separator may include anelectrolyte including a lithium salt and an organic solvent.

The lithium salt-containing nonaqueous electrolyte may include anonaqueous electrolyte and a lithium salt. The nonaqueous electrolytemay be a nonaqueous liquid electrolyte, an organic solid electrolyte, oran inorganic solid electrolyte.

The nonaqueous liquid electrolyte may include an organic solvent. Theorganic solvent may be any suitable organic solvent. For example, theorganic solvent may be propylene carbonate, ethylene carbonate,fluoroethylene carbonate, butylene carbonate, dimethyl carbonate,diethyl carbonate, methyl ethyl carbonate, methylpropyl carbonate,ethylpropyl carbonate, methylisopropyl carbonate, dipropyl carbonate,dibutyl carbonate, chloroethylene carbonate, benzonitrile, acetonitrile,tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone,1,3-dioxolane, 4-methyldioxolane, N,N-dimethyl formamide, N,N-dimethylacetamide, dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane,dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethylether, or a combination thereof.

For example, the lithium salt may be LiPF₆, LiBF₄, LiSbF₆, LiAsF₆,LiClO₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, Li(FSO₂)₂N, LiC₄F₉SO₃, LiAlO₂, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein x and y are naturalnumbers), LiCl, LiI, or a combination thereof. For example, to improvecharge-discharge characteristics and resistance to flame in a lithiummetal battery, pyridine, triethylphosphate, triethanolamine, cyclicether, ethylene diamine, n-glyme, hexamethyl phosphoramide, nitrobenzenederivative, sulfur, a quinone imine dye, N-substituted oxazolidinone,N,N-substituted imidazolidine, ethylene glycol dialkyl ether, anammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, or acombination thereof, may be added to the nonaqueous electrolyte. In someembodiments, to provide nonflammable characteristics, ahalogen-containing solvent such as carbon tetrachloride, ethylenetrifluoride, or the like may be further added to the nonaqueouselectrolyte.

For example, the lithium metal battery according to any one of theabove-described embodiments may have improved capacity and improvedlifetime characteristics, and thus may be used in a battery cell for useas a power source of a small device. The lithium metal battery may alsobe used as a unit battery of a medium-large size battery pack or batterymodule that include a plurality of battery cells for use as a powersource of a medium-large size device.

Examples of the medium-large size device are electric vehicles (EVs),including hybrid electric vehicles (HEVs) and plug-in hybrid electricvehicles (PHEVs); electric two-wheeled vehicles, including E-bikes andE-scooters; power tools; power storage devices; and the like, but arenot limited thereto.

As used herein, the term “alkyl” refers to a completely saturatedbranched or unbranched (or straight-chained or linear) hydrocarbon grouphaving the specified number of carbon atoms and having a valence of atleast one. Non-limiting examples of the “alkyl” group include methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl,isopentyl, neopentyl, iso-amyl, n-hexyl, 3-methylhexyl,2,2-dimethylpentyl, 2,3-dimethylpentyl, and n-heptyl.

At least one hydrogen atom of the alkyl group may be substituted with ahalogen atom, a C1-C20 alkyl group substituted with a halogen atom (forexample, CCF₃, CHCF₂, CH₂F, CCl₃, and the like), a C1-C20 alkoxy group,a C2-C20 alkoxyalkyl group, a hydroxyl group, a nitro group, a cyanogroup, an amino group, an amidino group, a hydrazine group, a hydrazonegroup, a carboxyl group or a salt thereof, a sulfonyl group, a sulfamoylgroup, a sulfonic acid group or a salt thereof, a phosphoric acid groupor a salt thereof, a C1-C20 alkyl group, a C2-C20 alkenyl group, aC2-C20 alkynyl group, a C1-C20 heteroalkyl group, a C6-C20 aryl group, aC7-C20 arylalkyl group, a C6-C20 heteroaryl group, a C7-C20heteroarylalkyl group, a C6-C20 heteroaryloxyl group, a C6-C20heteroaryloxyalkyl group, or a C6-C20 heteroarylalkyl group.

The term “halogen atom” indicates fluorine, bromine, chlorine, iodine,and the like.

As used herein, the term “alkenyl” group indicates a branched orunbranched hydrocarbon group that includes at least one carbon-carbondouble bond and has a valence of at least one. Non-limiting examples ofthe alkenyl group are vinyl, allyl, butenyl, isopropenyl, andisobutenyl. At least one hydrogen atom in the alkenyl group may besubstituted with any of the substituents for the alkyl group asdescribed above as long as the valence of the alkenyl group is notexceeded.

As used herein, the term “alkynyl” indicates a branched or unbranchedhydrocarbon group with at least one carbon-carbon triple bond.Non-limiting examples of the “alkynyl” group are ethynyl, butynyl,isobutynyl, and propynyl. At least one hydrogen atom of the “alkynyl”group may be substituted with any of the substituents for the alkylgroup as described above.

The term “aryl” means a cyclic group in which all ring members arecarbon and at least one ring is aromatic. More than one ring may bepresent and any additional rings may be independently aromatic,saturated, or partially unsaturated, and may be fused, pendant,spirocyclic or a combination thereof. Non-limiting examples of the“aryl” group are phenyl, naphthyl, and tetrahydronaphthyl. At least onehydrogen atom of the “aryl” group may be substituted with any of thesubstituents for the alkyl group as described above.

As used herein, the term “heteroaryl” group indicates a monocyclic orbicyclic organic group that includes one or more aromatic rings, inwhich at least one ring member is a heteroatom selected from nitrogen(N), oxygen (O), phosphorous (P), and sulfur (S), wherein the rest ofthe cyclic atoms are all carbon. The heteroaryl group may include, forexample, one to five heteroatoms, and in some embodiments, may include afive- to ten-membered ring. In the heteroaryl group, S or N may bepresent in various oxidized forms. Non-limiting examples of theheteroaryl group are thienyl, furyl, pyrrolyl, imidazolyl, pyrazolyl,thiazolyl, isothiazolyl, 1,2,3-oxadiazolyl, 1,2,4-oxadiazolyl,1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, 1,2,3-thiadiazolyl,1,2,4-thiadiazolyl, 1,2,5-thiadiazolyl, 1,3,4-thiadiazolyl,isothiazol-3-yl, isothiazol-4-yl, isothiazol-5-yl, oxazol-2-yl,oxazol-4-yl, oxazol-5-yl, isoxazol-3-yl, isoxazol-4-yl, isoxazol-5-yl,1,2,4-triazol-3-yl, 1,2,4-triazol-5-yl, 1,2,3-triazol-4-yl,1,2,3-triazole-5-yl, tetrazolyl, pyridine-2-yl, pyridine-3-yl,pyrazine-2-yl, pyrazine-4-yl, pyrazine-5-yl, pyrimidine-2-yl,pyrimidine-4-yl, and pyrimidin-5-yl.

The term “heteroaryl” includes a heteroaromatic ring that is selectivelyfused to at least one of an aryl group, a cycloaliphatic group, and aheterocyclic group.

As used herein, the term “carbocyclic” group indicates a saturated orpartially unsaturated non-aromatic monocyclic, bicyclic or tricyclichydrocarbon group. Non-limiting examples of the monocyclic hydrocarbongroup are cyclopentyl, cyclopentenyl, cyclohexyl, and cyclohexenyl.Non-limiting examples of the bicyclic hydrocarbon group are bornyl,decahydronaphthyl, bicyclo[2.1.1]hexyl, bicyclo[2.2.1]heptyl,bicyclo[2.2.1]heptenyl, or bicyclo[2.2.2]octyl. A non-limiting exampleof the tricyclic hydrocarbon is adamantly.

As used herein, the term “heterocyclic” group indicates a C5-C20 cyclichydrocarbon group, for example, C5-C10 cyclic group, including at leastone hetero atom. For example, the at least one hetero atom is selectedfrom S, N, O, and B.

As used herein, the terms “alkoxy,” “aryloxy,” and “heteroaryloxy,”indicate alkyl, aryl, and heteroaryl groups, respectively, which arebound to an oxygen atom.

One or more embodiments of the present disclosure will now be describedin further detail with reference to the following examples. However,these examples are only for illustrative purposes and are not intendedto limit the scope of the one or more embodiments of the presentdisclosure.

EXAMPLES Example 1: Manufacture of Negative Electrode

Poly(styrene-b-divinylbenzene) copolymer microspheres (having an averageparticle diameter of about 3 μm, available from EPRUI Nanoparticles &Microspheres Co., Ltd.) were added to anhydrous tetrahydrofuran toobtain a 5 weight percent (wt %)-block copolymer-containing mixture.

The block copolymer in the block copolymer-containing mixture included apolystyrene block and a polydivinylbenzene block in a mixed ratio ofabout 80:20 (4:1) by weight, and the poly(styrene-b-divinylbenzene)copolymer had a weight average molecular weight of about 100,000Daltons.

Lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO₂F)₂) was added to theblock copolymer-containing mixture to obtain a protective layer-formingcomposition. The amount of LiFSI was about 30 parts by weight based on100 parts by weight of the poly(styrene-b-divinylbenzene) copolymer.

The protective layer-forming composition was coated on a lithium metalthin film (having a thickness of about 20 μm) to a thickness of about 3μm with a doctor blade, dried at about 25° C., and then further dried ina vacuum at about 40° C. for about 24 hours, thereby to form a negativeelectrode with a protective layer on the lithium metal thin film.

Examples 2 and 3: Manufacture of Negative Electrodes

Negative electrodes were manufactured in the same manner as in Example1, except that the thicknesses of the protective layers were changed toabout 1 μm and about 8 μm, respectively.

Example 4: Manufacture of Negative Electrode

A negative electrode was manufactured in the same manner as in Example1, except that a poly(acrylonitrile-b-butadiene-b-styrene) blockcopolymer was further added to the protective layer-forming composition.

The amount of the poly(acrylonitrile-b-butadiene-b-styrene) copolymerwas about 2 parts by weight based on 100 parts by weight of thepoly(styrene-b-divinylbenzene) copolymer. Thepoly(acrylonitrile-b-butadiene-b-styrene) copolymer had a weight averagemolecular weight of about 100,000 Daltons, and had a mixed weight ratioof a polyacrylonitrile block, a polybutadiene block, and a polystyreneblock of about 25:25:50.

Example 5: Manufacture of Negative Electrode

A negative electrode was manufactured in the same manner as in Example4, except that the amount of thepoly(acrylonitrile-b-butadiene-b-styrene) copolymer was changed to 1part by weight based on 100 parts by weight of thepoly(styrene-b-divinylbenzene) copolymer.

Examples 6 and 7: Manufacture of Negative Electrodes

A negative electrode was manufactured in the same manner as in Example1, except that the poly(styrene-b-divinylbenzene) copolymer microsphereshad an average particle diameter of about 1.3 μm and about 8 μm,respectively.

Example 8: Manufacture of Negative Electrode

A negative electrode was manufactured in the same manner as in Example1, except that poly(styrene-b-divinylbenzene) copolymer microspheresincluding a polystyrene block and a polydivinylbenzene block in a mixedweight ratio of about 98:2 (49:1) were used.

Example 9: Manufacture of Lithium Metal Battery

The protective layer-forming composition prepared in Example 1 wascoated on a lithium metal thin film (having at a thickness of about 20μm) to a thickness of about 5 μm with a doctor blade, dried at about 25°C., and thermally treated in a vacuum at about 40° C., to form anegative electrode with a protective layer on the lithium metal thinfilm.

LiCoO₂, a conducting agent (Super-P; Timcal Ltd.), polyvinylidenefluoride (PVdF), and N-methylpyrrolidone were mixed together to obtain apositive active material layer-forming composition. A mixed weight ratioof LiCoO₂, the conducting agent, and PVdF in the positive activematerial layer-forming composition was about 97:1.5:1.5. The amount ofN-methylpyrrolidone was about 137 g with respect to 97 g of LiCoO₂.

The positive active material layer-forming composition was coated on analuminum foil (having a thickness of about 15 μm), dried at about 25°C., and further dried in a vacuum at about 110° C., to manufacture apositive electrode.

The positive electrode and the negative electrode (having a thickness ofabout 20 μm) manufactured according to the above-described processeswere assembled with a polyethylene separator (having a porosity of about48%) therebetween, to manufacture a lithium metal battery (pouch cell).

A liquid electrolyte was added between the positive electrode and thenegative electrode. The liquid electrolyte was an electrolyte including1.0M LiN(SO₂F)₂ (LiFSI) in a mixed solvent of 1,2-dimethoxyethane (DME)and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) in avolume ratio of about 2:8.

Examples 10 to 16: Manufacture of Lithium Metal Batteries

Lithium metal batteries were manufactured in the same manner as inExample 9, except that the negative electrodes of Examples 2 to 8 wereused, respectively, instead of the negative electrode of Example 1.

Example 17: Manufacture of Lithium Metal Battery

A lithium metal battery was manufactured in the same manner as inExample 12, except that LiNi_(0.6)Co_(0.2)Al_(0.2)O₂, instead of LiCoO₂,was used to prepare the positive active material layer-formingcomposition.

Example 18: Manufacture of Negative Electrode

A negative electrode was manufactured in the same manner as in Example1, except that poly(styrene-b-divinylbenzene) copolymer microsphereshaving an average particle diameter of about 50 μm were used.

Example 19: Manufacture of Negative Electrode

A negative electrode was manufactured in the same manner as in Example1, except that poly(styrene-b-divinylbenzene) copolymer microspheresincluding a polystyrene block and a polydivinylbenzene block in a mixedweight ratio of about 95:5, instead of 80:20, were used.

Examples 20 and 21: Manufacture of Lithium Metal Batteries

Lithium metal batteries were manufactured in the same manner as inExample 9, except that the negative electrodes of Examples 18, and 19,instead of the negative electrode of Example 1, were used, respectively.

Example 22: Manufacture of Negative Electrode

A negative electrode was manufactured in the same manner as in Example1, except that a 1:1 mixture (by weight) ofpoly(styrene-b-divinylbenzene) copolymer microspheres having an averageparticle diameter of about 3 μm and poly(styrene-b-divinylbenzene)copolymer microspheres having an average particle diameter of about 8 μmwas used, instead of using only poly(styrene-b-divinylbenzene) copolymermicrospheres having an average particle diameter of about 3 μm.

Example 23: Manufacture of Lithium Metal Battery

A negative electrode was manufactured in the same manner as in Example1, and a lithium metal battery was manufactured in the same manner as inExample 9 by using the negative electrode, except that a 1:1:1 mixture(by weight) of poly(styrene-b-divinylbenzene) copolymer microsphereshaving average particle diameters of about 3 μm, 3.09 μm, and 2.91 μmwas used, instead of poly(styrene-b-divinylbenzene) copolymermicrospheres having an average particle diameter of about 3 μm.

Example 24: Manufacture of Lithium Metal Battery

A negative electrode was manufactured in the same manner as in Example1, and a lithium metal battery was manufactured in the same manner as inExample 9 by using the negative electrode, except that a 1:1:1 mixture(by weight) of poly(styrene-b-divinylbenzene) copolymer microsphereshaving average particle diameters of about 3 μm, 2.82 μm, and 3.18 μmwas used, instead of poly(styrene-b-divinylbenzene) copolymermicrospheres having an average particle diameter of about 3 μm.

Example 25: Manufacture of Lithium Metal Battery

A negative electrode was manufactured in the same manner as in Example1, and a lithium metal battery was manufactured in the same manner as inExample 9 by using the negative electrode, except that a 1:1:1 mixture(by weight) of poly(styrene-b-divinylbenzene) copolymer microsphereshaving average particle diameters of about 3 μm, 2.7 μm, and 3.3 μm wasused, instead of poly(styrene-b-divinylbenzene) copolymer microsphereshaving an average particle diameter of about 3 μm.

Example 26: Manufacture of Negative Electrode

A negative electrode was manufactured in the same manner as in Example1, except that a 9:1 mixture (by weight) ofpoly(styrene-b-divinylbenzene) copolymer microspheres having a particlediameter of about 8 μm and poly(styrene-b-divinylbenzene) copolymermicrospheres having an average particle diameter of about 3 μm was used,instead of poly(styrene-b-divinylbenzene) copolymer microspheres havingan average particle diameter of about 3 μm.

Example 27: Manufacture of Negative Electrode

A negative electrode was manufactured in the same manner as in Example1, except that a 9:1 mixture (by weight) ofpoly(styrene-b-divinylbenzene) copolymer microspheres having an averageparticle diameter of about 3 μm and poly(styrene-b-divinylbenzene)copolymer microspheres having an average particle diameter of about 1.3μm was used, instead of poly(styrene-b-divinylbenzene) copolymermicrospheres having an average particle diameter of about 3 μm.

Example 28: Manufacture of Lithium Metal Battery

A negative electrode was manufactured in the same manner as in Example1, and a lithium metal battery was manufactured in the same manner as inExample 9 by using the negative electrode, except that a 1:1:1 mixture(by weight) of poly(styrene-b-divinylbenzene) copolymer microspherehaving average particle diameter of about 50 μm was used, instead ofpoly(styrene-b-divinylbenzene) copolymer microspheres having an averageparticle diameter of about 3 μm.

Example 29: Manufacture of Lithium Metal Battery

A negative electrode was manufactured in the same manner as in Example1, and a lithium metal battery was manufactured in the same manner as inExample 9 by using the negative electrode, except that a 1:1:1 mixture(by weight) of poly(styrene-b-divinylbenzene) copolymer microspherehaving average particle diameters of about 100 μm was used, instead ofpoly(styrene-b-divinylbenzene) copolymer microspheres having an averageparticle diameter of about 3 μm.

Comparative Example 1: Manufacture of Lithium Metal Battery

LiCoO₂, a conducting agent (Super-P; Timcal Ltd.), PVdF, andN-methylpyrrolidone were mixed together to obtain a positive activematerial layer-forming composition. A mixed weight ratio of LiCoO₂, theconducting agent, and PVdF in the positive active material layer-formingcomposition was about 97:1.5:1.5.

The positive active material layer-forming composition was coated on analuminum foil (having a thickness of about 15 μm), dried at about 25°C., and further dried in a vacuum at about 110° C., to manufacture apositive electrode.

The positive electrode manufactured according to the above-describedprocesses and a lithium metal electrode (having a thickness of about 20μm) were assembled with a polyethylene separator (having a porosity ofabout 48%) therebetween, thereby to manufacture a lithium metal battery.A liquid electrolyte was added between the positive electrode and thelithium metal electrode.

The liquid electrolyte was an electrolyte including 1.0M LiN(SO₂F)₂(LiFSI) in a mixed solvent of 1,2-dimethoxyethane (DME) and1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) in avolume ratio of about 2:8.

Comparative Example 2

Polystyrene was added to anhydrous tetrahydrofuran to obtain a 5 wt%-polystyrene-including mixture. The polystyrene had a weight averagemolecular weight of about 100,000 Daltons.

Lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO₂F)₂) was added to thepolystyrene-including mixture to obtain a protective layer-formingcomposition. The amount of LiFSI was about 30 parts by weight based on100 parts by weight of the polystyrene.

The protective layer-forming composition was coated on a lithium metalthin film (having a thickness of about 20 μm) to a thickness of about 3μm with a doctor blade, dried at about 25° C., and then further dried ina vacuum at about 40° C. for about 24 hours, thereby to form a negativeelectrode with a protective layer on the lithium metal thin film.

Comparative Examples 3 and 4

Negative electrodes with protective layer were manufactured in the samemanner as in Example 1, except that poly(styrene-b-divinylbenzene)copolymer microspheres having an average particle diameter of about 1 μmand about 0.2 μm, were used, respectively, to obtain the protectivelayer-forming composition.

Evaluation Example 1: Scanning Electron Microscopic (SEM) Analysis 1)Example 1 and 4

Surface status of each of the negative electrodes of Examples 1 and 4was analyzed using scanning electron microscopy (SEM).

SEM images of the negative electrode of Example 1 are shown in FIGS. 2Aand 2D, and SEM images of the negative electrode of Example 4 are shownin FIGS. 3A to 3C.

Referring to FIGS. 2A to 2D, the negative electrode of Example 1 wasfound to have a single layer structure of microspheres on a surface ofthe lithium metal thin film. Due to this arrangement of themicrospheres, no aggregation of the microspheres occurred.

Referring to FIGS. 3A to 3C, in the negative electrode of Example 4, theprotective layer on a surface of the lithium metal thin film was foundto have a monodisperse single layer structure of microspheres in closedpacked arrangement. The protective layer of FIG. 3A was a monodispersesingle layer, and the protective layers of FIGS. 3b and 3C had adouble-layer structure.

2) Example 22

Surface status of the negative electrode of Example 22 was analyzedusing SEM. An SEM image of the negative electrode of Example 22 is shownin FIG. 3D.

Referring to FIG. 3D, the negative electrode of Example 22 was found toinclude uniformly dispersed microspheres of the two different sizes onthe lithium metal thin film.

Evaluation Example 2: Lithium Deposition Density and SEM Analysis 1)Examples 9, 12, 28, and 29 and Comparative Examples 1 to 4

Each of the lithium metal batteries of Example 9, Example 12, Example28, Example 29, and Comparative Examples 1 to 4 was charged with aconstant current of 0.1C (0.38 mA/cm²) at about 25° C. until a voltageof about 4.40 V (with respect to Li), and maintained at a constantvoltage of 4.40 V (constant voltage mode) until a cutoff current of0.05C rate. This one-time charging was followed by measuring externalpouch thickness changes in the lithium metal batteries and a thicknessdeviation in a lithium deposition layer of each of the lithium metalbatteries with a lithium micrometer. The results are shown in Table. 1.Lithium deposition density was also evaluated by measuring the thicknessof the lithium deposition layer on the negative electrode of each of thelithium metal batteries. The results are shown in Table 2.

TABLE 1 Change in external Thickness deviation of pouch thicknesslithium deposition layer Example (μm) (μm) Example 9  38-40  ±3 Example12 30-31  ±3 Comparative Example 1 50-60 ±10 Comparative Example 2 50±10 Comparative Example 3 42-43  ±3 Comparative Example 4 46-48  ±5

Referring to Table 1, the lithium metal batteries of Examples 9 and 12were found to have a small change in external pouch thickness, comparedto the lithium metal batteries of Comparative Examples 1 to 4. Also, thelithium metal batteries of Examples 9 and 12 were found to have areduced thickness deviation of the lithium deposition layer, compared tothe lithium metal batteries of Comparative Examples 1, 2, and 4.

The lithium metal batteries of Examples 9 and 12 were found to have anincreased thickness uniformity at different measurement points, comparedto the lithium metal batteries of Comparative Examples 1 to 4.

The lithium metal batteries of Examples 28 and 29 were found to have asmall change in external pouch thickness, compared to the lithium metalbatteries of Comparative Examples 1 to 4.

TABLE 2 Lithium deposition density Thickness of lithium Example (g/cc org/cm³) deposition layer (μm) Example 9  0.207-0.225 35-38 Example 120.260-0.270 28-30 Comparative Example 1 0.134-0.161 45 ComparativeExample 2 0.134 50 Comparative Example 3 0.18-0.20 39-41 ComparativeExample 4 0.17-0.18 44-46

Referring to Table 2, the lithium metal batteries of Examples 9 and 12were found to have a higher lithium deposition density by about 50% orgreater, compared to the lithium deposition density of the lithium metalbattery of Comparative Example 1. Also, the lithium metal batteries ofExamples 9 and 12 were found to have an increased deposition density,compared to those of the lithium metal batteries of Comparative Examples2 to 4 and to have a reduced thickness of the lithium deposition layercompared to those of the lithium metal batteries of Comparative Examples1 to 4.

After each of the lithium metal batteries of Example 9 and ComparativeExample 1 was charged with a constant current of 0.1C rate at about 25°C. until a voltage of about 4.40 V (with respect to Li), a cross-sectionstatus of each of the lithium metal electrodes, on which a lithiumdeposition layer was formed, was analyzed using SEM.

FIGS. 4A and 5A are schematic views of the lithium metal batteries ofExample 9 and Comparative Example 1, respectively, in which the lithiumnegative electrode of each of the lithium metal batteries was formed ona copper thin film used as a negative electrode current collector.

Referring to FIG. 4A, the negative electrode of the lithium metalbattery of Example 9 had a stack structure in which a lithium metalelectrode 41 was formed on a negative electrode current collector 40,and a protective layer 42 including polystyrene microspheres 43 wasstacked on the lithium metal electrode 41.

The SEM results are shown in FIGS. 4B to 4D and FIGS. 5B to 5D. FIGS. 4Band 4C are SEM images of a surface of the negative electrode 41 of thelithium metal battery of Example 9. FIGS. 5B and 5C are SEM images of asurface of a negative electrode of the lithium metal battery ofComparative Example 1.

Referring to FIG. 5A, the negative electrode of the lithium metalbattery of Comparative Example 1 had a structure in which a lithiummetal electrode 51 was stacked on a negative electrode current collector50, and lithium dendrites 52 were randomly formed on the lithium metalelectrode 51. This random growth of lithium dendrites on the lithiummetal electrode 51 in the lithium metal battery of Comparative Example 1is shown in FIGS. 5B and 5C.

However, unlike the lithium metal battery of Comparative Example 1 shownin FIGS. 5B and 5C, nearly no lithium dendrite was grown in the lithiummetal battery of Example 9, as shown in FIGS. 4B and 4C. The lithiummetal battery of Example 9 was also found to include a compact lithiumdeposition layer with a high density as shown in FIG. 4D, unlike thelithium metal battery of Comparative Example 1 shown in FIG. 5D.

2) Examples 23 to 25

Each of the lithium metal batteries of Examples 23 to 25 was chargedwith a constant current of 0.1C (0.38 mA/cm²) at about 25° C. until avoltage of about 4.40 V (with respect to Li), and maintained at aconstant voltage of 4.40 V (constant voltage mode) until a cutoffcurrent of 0.05C rate. This one-time charging was followed by measuringexternal pouch thickness changes in the lithium metal batteries and athickness deviation in a lithium deposition layer of each of the lithiummetal batteries with a lithium micrometer. The results are shown inTable 3. Lithium deposition density was also evaluated by measuring thethickness of the lithium deposition layer on the negative electrode ofeach of the lithium metal batteries. The results are shown in Table 3.

In Table 3, the particle diameter difference of thepoly(styrene-b-divinylbenzene) copolymer microspheres (MS) wascalculated according to the following equation.

Particle diameter difference of MS (%)={(Maximum particle diameter ofMS−average

particle diameter of particle)/average particle diameter of MS}×100%

TABLE 3 External Thickness Thickness Particle pouch deviation of Lithiumof diameter thickness lithium deposition lithium difference changedeposition density deposition of MS (%) (μm) layer (μm) (g/cc)(g/cm3)layer (μm) Example 23 30-31 ±3 0.260-0.270 28-30 (±3%) Example 24 31-33±3 0.245-0.260 29-31 (±6%) Example 25 32-35 ±3 0.225-0.255 30-33 (±10%)

3) Examples 26 and 27

Lithium deposition densities, external pouch changes thickness, andthicknesses and deviations of lithium deposition layers of the lithiummetal batteries of Examples 26 and 27 were measured, and the results areshown in Table 4.

TABLE 4 External Thickness pouch deviation of Lithium Thickness ofthickness lithium deposition lithium change deposition densitydeposition Example (μm) layer (μm) (g/cc)(g/cm³) layer (μm) Example 2631-33 ±4 0.255-0.265 29-31 Example 27 29-31 ±3 0.270-0.280 27-29

Evaluation Example 3: Impedance Measurement

Impedance measurements were performed on the lithium metal batteries ofExample 17 and Comparative Example 1 were measured with a Solartron1260A Impedance/Gain-Phase Analyzer in a frequency range of about 0.1 Hzto about 1 MHz and an amplitude of about ±10 mV, to measure resistanceat about 25° C. by a 2-probe method.

Nyquist plots obtained from the impedance measurements that wereperformed after 24 hours from the manufacture of the lithium metalbatteries of Example 17 and Comparative Example 1 are shown in FIG. 6.In FIG. 6, an interfacial resistance between the negative electrode andthe electrolyte depends from the positions and sizes of semicircles.

Referring to FIG. 6, the lithium metal battery of Example 17 was foundto have a lower interfacial resistance compared to the lithium metalbattery of Comparative Example 1.

Evaluation Example 4: Charge-Discharge Characteristics (DischargeCapacity) 1) Example 9 and Comparative Example 1

Each of the lithium metal batteries of Example 9 and Comparative Example1 was charged at about 25° C. with a constant current of 0.1 C rate to avoltage of about 4.40 Volts (V) (with respect to Li), and then with aconstant voltage of 4.40 V until a cutoff current of 0.05C rate, and wasthen discharged with a constant current of 0.1 C rate to a voltage ofabout 2.8 V (with respect to Li) (Formation process, 1^(st) cycle). Thiscycle of charging and discharging was performed two times more tocomplete the formation process.

Each of the lithium metal batteries after the formation process wascharged at room temperature (25° C.) with a constant current of 0.7 C toa voltage range of about 3.0 V to 4.4 V (with respect to Li) and thendischarged with a current of 0.5C until a cutoff voltage of 3.0 V.

This cycle of charging and discharging was performed 100 times in total.The capacity retention rate of each of the lithium metal batteries wascalculated using Equation 1.

Capacity retention rate (%)=(100^(th) cycle discharge capacity/1^(st)cycle discharge capacity)×100%   Equation 1

The results of evaluating the capacity retention rates of the lithiummetal batteries are shown in FIG. 7.

Referring to FIG. 7, the lithium metal battery of Example 9 was found tohave a remarkably improved capacity retention rate, compared to thelithium metal battery of Comparative Example 1.

2) Example 17 and Comparative Example 1

Discharge capacities, capacity retention rates, and coulombicefficiencies of the lithium metal batteries of Example 17 andComparative Example 1 were measured. The results are shown in FIGS. 8Ato 8C.

Referring to FIGS. 8A to 8C, the lithium metal battery of Example 17 wasfound to have an improved discharge capacity, capacity retention rate,and coulombic efficiency, compared to the lithium metal battery ofComparative Example 1.

Evaluation Example 5: Tensile Modulus

After the protective layer-forming compositions of Examples 1 to 4 andComparative Examples 3 and 4 were each cast on a substrate,tetrahydrofuran (THF) in the resulting cast product was slowlyevaporated at about 25° C. for about 24 hours in an argon glove box,followed by drying under vacuum at about 25° C. for about 24 hours,thereby forming a protective layer in membrane form. The protectivelayer had a thickness of about 50 μm.

A tensile modulus of the protective layer was measured using a DMA800(available from TA Instruments). Protective layer samples for thetensile modulus measurement were prepared according to the ASTM standardD412 (Type V specimens). The tensile modulus is also known as Young'smodulus.

Variations in strain with respect to stress in the protective layer weremeasured at about 25° C., a relative humidity of about 30%, and a rateof 5 millimeters per minute (mm/min). The tensile modulus of theprotective layer was calculated from the slope of a stress-strain curvethereof.

As a result, the protective layers of Examples 1 to 4 were found to havea higher tensile modulus of about 10⁶ Pa or greater, compared to theprotective layers of Comparative Examples 3 and 4. Thus, using theprotective layer of Examples 1 to 4 with such improved characteristicsmay effectively suppress volumetric change of the lithium metal negativeelectrode and growth of lithium dendrite.

Evaluation Example 6: Ion Conductivity

Ion conductivities of the protective layers formed in Examples 1 and 2were measured as follows. The resistance in each of the protectivelayers was measured while scanning the temperature of the protectivelayer with a bias voltage of about 10 mV in a frequency range of about 1Hz to 1 MHz, thereby measuring the ion conductivity of the protectivelayer.

As a result, the protective layer of Example 1 was found to have goodion conductivity. The protective layer of Example 2 was also found tohave an ion conductivity equivalent to the ion conductivity of theprotective layer of Example 1.

As described above, according to the one or more embodiments, a negativeelectrode for a lithium metal battery may include a protective layerwith improved physical properties. Using this negative electrode, alithium metal battery with an effectively suppressed volumetric changeduring charging and improved cycle lifetime and discharge capacity maybe manufactured.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould be considered as available for other similar features or aspectsin other embodiments.

While one or more embodiments have been described with reference to thefigures, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. A negative electrode for a lithium metal battery,comprising: a lithium metal electrode comprising lithium metal or alithium metal alloy; and a protective layer comprising a liquidelectrolyte or a polymer ionic liquid, and a plurality of organicparticles having an average particle size of greater than 1 micrometerto about 100 micrometers, the protective layer disposed on at least aportion of the lithium metal electrode, wherein the protective layer hasa Young's modulus of about 10⁶ pascals to about 10¹¹ pascals.
 2. Thenegative electrode of claim 1, wherein the liquid electrolyte comprisesa lithium salt, an ionic liquid, an organic solvent, or a combinationthereof.
 3. The negative electrode of claim 2, wherein the ionic liquidcomprises: a cation comprising an ammonium cation, a pyrrolidiniumcation, a pyridinium cation, a pyrimidinium cation, an imidazoliumcation, a piperidinum cation, a pyrazolium cation, an oxazolium cation,a pyridazinium cation, a phosphonium cation, a sulfonium cation, atriazolium cation, or a combination thereof; and an anion comprising BF₄⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻, ClO₄ ⁻, CH₃SO₃ ⁻, CF₃CO₂ ⁻,Cl⁻, Br⁻, I⁻, BF₄ ⁻, SO₄ ²⁻, CF₃SO₃ ⁻, (FSO₂)₂N⁻, (C₂F₅SO₂)₂N⁻,(C₂F₅SO₂)(CF₃SO₂)N⁻, (CF₃SO₂)₂N⁻, or a combination thereof, and whereinthe liquid electrolyte further comprises a lithium salt, and the lithiumsalt comprises LiSCN, LiN(CN)₂, LiClO₄, LiBF₄ ⁻, LiAsF₆, LiPF₆,LiCF₃SO₃, LiC(CF₃SO₂)₃, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)₂, LiN(SO₂F)₂, LiSbF₆,LiPF₃(CF₂CF₃)₃, LiPF₃(CF₃)₃, LiB(C₂O₄)₂, or a combination thereof. 4.The negative electrode of claim 2, wherein the organic solvent comprisesa carbonate compound, a glyme compound, and a dioxolane compound, or theorganic solvent comprises ethylene carbonate, propylene carbonate,dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate,fluoroethylene carbonate, or a combination thereof, or the organicsolvent comprises γ-butyrolactone, 1,2-dimethoxy ethane, 1,2-diethoxyethane, dimethylene glycol dimethyl ether, trimethylene glycol dimethylether, tetra(ethylene glycol)dimethyl ether, tri(ethyleneglycol)dimethyl ether, poly(ethylene glycol)dilaurate, poly(ethyleneglycol)monoacrylate, poly(ethylene glycol)diacrylate, polyethyleneglycol dimethyl ether, succinonitrile, sulfolane, dimethyl sulfone,ethyl methyl sulfone, diethyl sulfone, adiponitrile, tetraethyleneglycoldimethyl ether, 1,3-dioxolane, 4,5-diethyl-1,3-dioxolane,4,5-dimethyl-1,3-dioxolane, 4-methyl-1,3-dioxolane,4-ethyl-1,3-dioxolane, 2,2-dimethoxy-2-phenyl acetophenone,dimethylether, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran,1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether or acombination thereof.
 5. The negative electrode of claim 1, wherein theprotective layer comprising the polymer ionic liquid further comprises alithium salt.
 6. The negative electrode of claim 1, wherein the polymerionic liquid comprises a repeating unit comprising: a cation comprisingan ammonium cation, a pyrrolidinium cation, a pyridinium cation, apyrimidinium cation, an imidazolium cation, a piperidinum cation, apyrazolium cation, an oxazolium cation, a pyridazinium cation, aphosphonium cation, a sulfonium cation, a triazolium cation, or acombination thereof, and an anion comprising BF₄, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻,AlCl₄ ⁻, HSO₄, ClO₄ ⁻, CH₃SO₃ ⁻, CF₃CO₂ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻, Cl⁻,Br⁻, I⁻, SO₄ ²⁻, CF₃SO₃ ⁻, (C₂F₅SO₂)₂N⁻, (C₂F₅SO₂)(CF₃SO₂)N⁻, NO₃ ⁻,Al₂Cl₇ ⁻, (CF₃SO₂)₃ ⁻, (CF₃)₂PF₄ ⁻, (CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻,(CF₃)₆P⁻, SF₅CF₂SO₃ ⁻, SF₅CHFCF₂SO₃ ⁻, CF₃CF₂(CF₃)₂CO⁻, (CF₃SO₂)₂CH⁻,(SF₅)₃C⁻, (O(CF₃)₂C₂(CF₃)₂O)₂PO⁻, or a combination thereof.
 7. Thenegative electrode of claim 1, where in the liquid electrolyte occupiesabout 30 volume percent to about 60 volume percent of the total volumeof the protective layer.
 8. The negative electrode of claim 1, whereinthe organic particles comprise a polystyrene homopolymer, a copolymerhaving a weight average molecular weight of about 10,000 Daltons toabout 100,000 Daltons and comprising a styrene repeating unit, or acombination of the polystyrene homopolymer and the copolymer.
 9. Thenegative electrode of claim 8, wherein the copolymer comprises apoly(styrene-divinylbenzene) copolymer, a poly(methylmethacrylate-divinylbenzene) copolymer, a poly(ethylmethacrylate-divinylbenzene) copolymer, a poly(pentylmethacrylate-divinylbenzene) copolymer, a poly(butylmethacrylate-divinylbenzene) copolymer, a poly(propylmethacrylate-divinylbenzene) copolymer, apoly(styrene-ethylene-butylene-styrene) copolymer, a poly(styrene-methylmethacrylate) copolymer, a poly(styrene-acrylonitrile) copolymer,poly(styrene-vinylpyridine) copolymer, apoly(acrylonitrile-butadiene-styrene) copolymer, apoly(acrylonitrile-ethylene-propylene-styrene) copolymer, a poly(methylmethacrylate-acrylonitrile-butadiene-styrene) copolymer, a poly((C1-C9alkyl) methacrylate-butadiene-styrene) copolymer, a poly(styrene-(C1-C9alkyl) acrylate) copolymer, a poly(acrylonitrile-styrene-(C1-C9 alkyl)acrylate) copolymer, or a combination thereof; and wherein the styrenerepeating unit of the copolymer is from about 65 to 99 parts by weight,based on 100 parts by weight of the copolymer, and in the copolymer ifthe styrene repeating unit is a divinylbenzene repeating unit, an amountof divinylbenzene is in a range of from about 1 to 35 parts by weight,based on 100 parts by weight of the copolymer.
 10. The negativeelectrode of claim 8, wherein the copolymer is a block copolymercomprising a poly(styrene-divinylbenzene) copolymer, a poly(methylmethacrylate-divinylbenzene) copolymer, a poly(ethylmethacrylate-divinylbenzene) copolymer, a poly(pentylmethacrylate-divinylbenzene) copolymer, a poly(butylmethacrylate-divinylbenzene) copolymer, a poly(propylmethacrylate-divinylbenzene) copolymer, apoly(styrene-ethylene-butylene-styrene) copolymer, a poly(styrene-methylmethacrylate) copolymer, a poly(styrene-acrylonitrile) copolymer, apoly(styrene-vinylpyridine) copolymer, apoly(acrylonitrile-butadiene-styrene) copolymer, apoly(acrylonitrile-ethylene-propylene-styrene) copolymer, a poly(methylmethacrylate-acrylonitrile-butadiene-styrene) copolymer, a poly((C1-C9alkyl) methacrylate-butadiene-styrene) copolymer, a poly(styrene-(C1-C9alkyl) acrylate) copolymer, a poly(acrylonitrile-styrene-(C1-C9 alkyl)acrylate) copolymer, or a combination thereof.
 11. The negativeelectrode of claim 1, wherein the protective layer has a porosity ofabout 25% to about 50%, based on a total volume of the protective layer.12. The negative electrode of claim 1, wherein the protective layer hasa thickness of about 1 micrometer to about 10 micrometers.
 13. Thenegative electrode of claim 1, wherein the plurality of particlescomprises particles having a cross-linked structure.
 14. The negativeelectrode of claim 12, wherein the particles having the cross-linkedstructure have a degree of cross-linking of about 10 percent to about 30percent, based on a total volume of the cross-linked polymer particle.15. The negative electrode of claim 1, wherein the protective layerfurther comprises an ion conductive polymer.
 16. The negative electrodeof claim 15, wherein the ion conductive polymer is a homopolymer or acopolymer, and wherein the ion conductive polymer is optionallycross-linked.
 17. The negative electrode of claim 15, wherein the ionconductive polymer is polystyrene homopolymer, a block copolymercomprising a styrene repeating unit, or a combination thereof.
 18. Alithium metal battery comprising: a positive electrode; the negativeelectrode of claim 1; and an electrolyte between the positive electrodeand the negative electrode, wherein the electrolyte between the positiveelectrode and the negative electrode comprises a liquid electrolyte, asolid electrolyte, a gel electrolyte, a polymer ionic liquid, or acombination thereof.
 19. The lithium metal battery of claim 18, whereinthe liquid electrolyte comprises a lithium salt and an organic solvent,and the liquid electrolyte occupies about 30 volume percent to about 60volume percent of the total volume of the protective layer.
 20. Thelithium metal battery of claim 18, wherein the electrolyte between thepositive electrode and the negative electrode comprises a solidelectrolyte comprising an organic solid electrolyte or an inorganicsolid electrolyte.
 21. The lithium metal battery of claim 20, whereinthe organic solid electrolyte comprises a polyethylene derivative, apolyethylene oxide derivative, a polypropylene oxide derivative, aphosphoric acid ester polymer, polyester sulfide, polyvinyl alcohol,polyfluoride vinylidene, a polymer including an ionic dissociativegroup, or a combination thereof, and wherein the inorganic solidelectrolyte comprises Li₃N, LiI, Li₅NI₂, Li₃N—LiI—LiOH, Li₂SiS₃,Li₄SiO₄, Li₄SiO₄—LiI—LiOH, Li₃PO₄—Li₂S—SiS₂, Cu₃N, LiPON,Li₂S.GeS₂.Ga₂S₃, Li₂O.11Al₂O₃, (Na,Li)_(1+x)Ti_(2−x)Al_(x)(PO₄)₃,wherein 0.1≤x≤0.9, Li_(1+x)Hf_(2−x)Al_(x)(PO₄)₃, wherein 0.1≤x≤0.9,Na₃Zr₂Si₂PO₁₂, Li₃Zr₂Si₂PO₁₂, Na₃Zr₂Si₂PO₁₂, Li₃Zr₂Si₂PO₁₂, Na₅ZrP₃O₁₂,Na₅TiP₃O₁₂, Na₃Fe₂P₃O₁₂, Na₄NbP₃O₁₂, sodium silicates,Li_(0.3)La_(0.5)Ti_(0.3), Na₅MSi₄O₁₂, wherein M is a rare earth element,Li₅ZrP₃O₁₂, Li₅TiP₃O₁₂, Li₃Fe₂P₃O₁₂, Li₄NbP₃O₁₂,Li_(1+x)(M,Al,Ga)_(x)(Ge_(1−y)T_(1−y))_(2−x)(PO₄)₃, wherein x≤1.8,0≤y≤1.0, and M is Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, or Yb,Li_(1+x+y)Q_(x)Ti_(2−x)Si_(y)P_(3−y)O₁₂, wherein 0<x≤0.4, 0<y≤01.6, andQ is Al or Ga, Li₆BaLa₂Ta₂O₁₂, Li₇La₃Zr₂O₁₂, Li₅La₃Nb₂O₁₂, Li₅La₃M₂O₁₂,wherein M is Nb or Ta, Li_(7+x)A_(x)La_(3−x)Zr₂O₁₂, wherein 0<x<3 and Ais Zn, or a combination thereof.
 22. The lithium metal battery of claim18, wherein a lithium deposition layer is disposed between theprotective layer and the negative electrode, and a thickness of thelithium deposition layer in the lithium metal battery is greater than 0micrometers to about 40 micrometers.
 23. The lithium metal battery ofclaim 18, wherein a lithium deposition layer is disposed between theprotective layer and the negative electrode, and a lithium depositiondensity of the lithium deposition layer is from about 0.2 grams percubic centimeter to about 0.3 grams per cubic centimeter.
 24. Thelithium metal battery of claim 18, wherein a lithium deposition layer isdisposed between the protective layer and the lithium metal electrode,and wherein the lithium metal battery has a lithium deposition densitywhich is about 50 percent to about 75 percent of a lithium depositiondensity of a lithium metal battery having a negative electrode withoutthe protective layer.
 25. The lithium metal battery of claim 18, furthercomprising a separator, and wherein the electrolyte is a liquidelectrolyte, and the lithium metal battery has a stack structure inwhich the negative electrode, the separator, the liquid electrolyte, andthe positive electrode are sequentially stacked upon one another in thisstated order.